I always wonder about testing like that... How did they arrive at those numbers? How can you assign a resolution number to a zoom? At what focal length was that determined and is it consistent across all focal lengths? Also, you can't test brands using the same camera... Canon lens needs to be tested on a Canon camera, Nikon lens on a Nikon cameras... how do they account for different cameras?

Enroll me in the "Show Me" school of thought (it's somewhere in Missouri, I think).

I like to look for myself, at sites like the-digital-picture.com

For example, I looked at lens test shots done with Canon 100-400mm "II" and Nikkor 200-500mm (on 50MP Canon 5Ds-R and 46MP Nikon D850, respectively).

https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=972&Camera=979&Sample=0&FLI=3&API=1&LensComp=1035&CameraComp=1210&SampleComp=0&FLIComp=1&APIComp=0

Those are the "most demanding" cameras Nikon and Canon make... the "toughest" on lenses with highest resolution. Looking at those two lenses at the focal lengths they share and "wide open" (usually a lens' "worst" aperture):

At 200mm... There's very little difference. Both lenses are quite sharp at image center, mid-frame and corner.

At 300mm... The Canon lens is slightly sharper at the center, moderately sharper at mid-frame and a lot sharper in the corner.

At 400mm... The Canon lens is moderately sharper at center, a lot sharper at mid-frame and a whole lot sharper in the corner.

At 560mm (Canon w/1.4X) and 500mm.... They're pretty close in terms of sharpness, but some chromatic aberration has appeared in the Nikon lens.

At 800mm (Canon w/2X) and 850mm (Nikon w/1.4X).... Both lenses are fairly sharp at the center, lose some sharpness similarly mid-frame and in the corners. Off center the Nikon lens gains a good deal of chromatic aberration. There's a very slight gain of CA in the corners with the Canon.

There's not much point looking at 100mm since the Nikon lens can't do it at all. This is where the Canon lens is at it's weakest... Sharpness is okay, but it picks up some chromatic aberration.

While image quality is important, there's more to lenses than that. The Canon lens is around $500 more expensive than the Nikon. Conversely, the Nikon lens is larger and heavier than the Canon (as might be expected considering the different focal length ranges). The Nikon is over 5 lb., more than 10" long and uses 95mm filters. The Canon is about 3.5 lb., around 8" long and uses 77mm filters.

The Nikon has a non-variable aperture... f/5.6 throughout (f/8 with 1.4X, 850mm). The Canon lens' aperture is variable.... f4.5 to approx. 135mm, f/5 to around 310mm, then f/5.6 the rest of the way to 400mm (f/8 with 1.4X, 560mm.... or f/11 with 2X, 800mm).

Both lenses are internal focusing.... they don't change length when focused closer. But neither lens is internal zooming... both increase in length about 3 inches when zoomed to longer focal lengths.

Both lenses use their respective manufacturer's highest performance autofocus drive systems: AF-S on the Nikon, USM on the Canon. I haven't compared them personally.... and the camera used with them, as well as user settings and skill all make a difference... But I would expect them to have similarly fast and capable AF.

Both lenses have image stabilization. I can't say a lot about the VR on the Nikon, but I do know that the IS on the Canon is the "latest and greatest" type. It's similar to what's used on the Canon super telephotos such as the EF 300mm f/2.8L IS USM II, etc. In fact, the 100-400mm II is the least expensive lens using this more advanced form of IS.

The Canon lens is part of their L-series, which are generally better built for durability and have some level of sealing for weather and dust resistance. The guys at Lensrentals.com love to take things apart just to see what's inside, and when they did that several years ago with the Canon 100-400mm II they called it "the best built zoom lens we've ever seen", noting a number of "over-engineered" parts used for durability and reliability. Without much experience with it and certainly never having disassembled one, I have no idea how the Nikon lens compares in this respect. But it seems to be pretty well built.

Rather than just trust some numbers, with any lens I'd make comparison similar to above. I'd want to look at actual, magnified test shots for image quality, distortion, flare, chromatic aberration, yada, yada. I'd also always consider all the other factors... besides image quality... that can weigh on a decision.

The various British photo magazines have been publishing these numbers this month and I finally broke down and purchased the "Digital Camera World" version.....($15) at Barnes & Noble. This is a short summary of the results that I thought many would have an interest in.
The first number is the Imatest scoring (interpolated from a graph) from the center of the image, at the max focal length wide open ( higher is better) and the second number is the "their" fringing score. ( lower is better).
Canon 100-400 II - 1700, ,03
Nikon 200-500 - 1800, 2.21
Sigma 60-600 - 1450, 1.42
Sigma 100-400 - 1550, 1.01
Sigma 150-600 C - 1500, 1.16
Sigma 150-600 S - 1650, 1.01
Tamron 100-400 - 1850, 1.11
Tamron 150-600 G2 - 1600, 1.91

Nikkor Z 14-30mm S - 2100-2800- .99-.36 !

..

I always wonder about testing like that... How did they arrive at those numbers? How can you assign a resolution number to a zoom? At what focal length was that determined and is it consistent across all focal lengths? Also, you can't test brands using the same camera... Canon lens needs to be tested on a Canon camera, Nikon lens on a Nikon cameras... how do they account for different cameras?

Enroll me in the "Show Me" school of thought (it's somewhere in Missouri, I think).

I like to look for myself, at sites like the-digital-picture.com

For example, I looked at lens test shots done with Canon 100-400mm "II" and Nikkor 200-500mm (on 50MP Canon 5Ds-R and 46MP Nikon D850, respectively).

https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=972&Camera=979&Sample=0&FLI=3&API=1&LensComp=1035&CameraComp=1210&SampleComp=0&FLIComp=1&APIComp=0

Those are the "most demanding" cameras Nikon and Canon make... the "toughest" on lenses with highest resolution. Looking at those two lenses at the focal lengths they share and "wide open" (usually a lens' "worst" aperture):

At 200mm... There's very little difference. Both lenses are quite sharp at image center, mid-frame and corner.

At 300mm... The Canon lens is slightly sharper at the center, moderately sharper at mid-frame and a lot sharper in the corner.

At 400mm... The Canon lens is moderately sharper at center, a lot sharper at mid-frame and a whole lot sharper in the corner.

At 560mm (Canon w/1.4X) and 500mm.... They're pretty close in terms of sharpness, but some chromatic aberration has appeared in the Nikon lens.

At 800mm (Canon w/2X) and 850mm (Nikon w/1.4X).... Both lenses are fairly sharp at the center, lose some sharpness similarly mid-frame and in the corners. Off center the Nikon lens gains a good deal of chromatic aberration. There's a very slight gain of CA in the corners with the Canon.

There's not much point looking at 100mm since the Nikon lens can't do it at all. This is where the Canon lens is at it's weakest... Sharpness is okay, but it picks up some chromatic aberration.

While image quality is important, there's more to lenses than that. The Canon lens is around $500 more expensive than the Nikon. Conversely, the Nikon lens is larger and heavier than the Canon (as might be expected considering the different focal length ranges). The Nikon is over 5 lb., more than 10" long and uses 95mm filters. The Canon is about 3.5 lb., around 8" long and uses 77mm filters.

The Nikon has a non-variable aperture... f/5.6 throughout (f/8 with 1.4X, 850mm). The Canon lens' aperture is variable.... f4.5 to approx. 135mm, f/5 to around 310mm, then f/5.6 the rest of the way to 400mm (f/8 with 1.4X, 560mm.... or f/11 with 2X, 800mm).

Both lenses are internal focusing.... they don't change length when focused closer. But neither lens is internal zooming... both increase in length about 3 inches when zoomed to longer focal lengths.

Both lenses use their respective manufacturer's highest performance autofocus drive systems: AF-S on the Nikon, USM on the Canon. I haven't compared them personally.... and the camera used with them, as well as user settings and skill all make a difference... But I would expect them to have similarly fast and capable AF.

Both lenses have image stabilization. I can't say a lot about the VR on the Nikon, but I do know that the IS on the Canon is the "latest and greatest" type. It's similar to what's used on the Canon super telephotos such as the EF 300mm f/2.8L IS USM II, etc. In fact, the 100-400mm II is the least expensive lens using this more advanced form of IS.

The Canon lens is part of their L-series, which are generally better built for durability and have some level of sealing for weather and dust resistance. The guys at Lensrentals.com love to take things apart just to see what's inside, and when they did that several years ago with the Canon 100-400mm II they called it "the best built zoom lens we've ever seen", noting a number of "over-engineered" parts used for durability and reliability. Without much experience with it and certainly never having disassembled one, I have no idea how the Nikon lens compares in this respect. But it seems to be pretty well built.

Rather than just trust some numbers, with any lens I'd make comparison similar to above. I'd want to look at actual, magnified test shots for image quality, distortion, flare, chromatic aberration, yada, yada. I'd also always consider all the other factors... besides image quality... that can weigh on a decision.