My experience has been different. I am a long time Nikon shooter, own (3 years, acquired for B&H AND Tokina direct) and use (4 days a week) the Tokina 24-70, 16-28, and 100 2.8 line up for weddings, sporting events, portrait shoots, and other large social gatherings. All perform as well as their Nikon counterparts at about 1/3 the price. Personal experience with Tokina support (only once) was flawless, as good as anything I ever experienced with NIKON. Tokina warranties their new lenses for 3 years. Nikon's warranty on lenses is 1 year. That matters to me.

I have the SB 400. Outstanding AND well built. Dropped often, not problems. Cannot say that about all Nikon flashes. Mine is about 11 years old. For off camera, I use a short coil, wired connection to the camera's hot shoe. Another $40. Well worth it.

If you are shooting wildlife, spending lots of time in one or two locations, and your needs dictate a tripod, then YES, Gimbal is an outstanding solution.

TWO suggestions;

--- Wimberely WH 200 has been my go to for heavy wildlife rigs for about 10 years. 400 2.8, 600 4.0 pro lenses PLUS Pro body. Wind, rain, snow. Still superb. But $$$ and really heavy. I would recommend the BIG W if and only if you have demanding professional requirements.

--- Jobu III jr. about $125-$150 used. Holds about 12-15 lbs just fine. Again, 10 years of field work. Outstanding.

From the view point as a part time professional photographer:
1) Owned this lens for about 7 years. No problems.
2) Traveled the world with it (14 countries) for months at a time, using it as my primary lens - D610, d800e
4) 1000s of terrific shots BUT definitely some soft spots ( wide open @ 120 is not that great but usable)
6) overall IQ is excellent
7) As a portrait lens, compared to my 100 2.8 Tokina, not preferred at all. BUT I have used it at events (when $$$ at stake) AND results were fine
7) solid weather sealing, not too heavy, well made
8) great value as a used lens at current price points
9) if this lens failed, would buy another

Yes. Their offer to me was laughable. D800e, 32K clicks, 9/10 overall condition (10 being "line new") was $68.

I use the FTZ adaptor to pair my sigma 100-400 with my Z50. Works great. Not a glitch.

Been using Wimberely WH200 for about 5 years. TWO HUNDRED+ shoots. Global travel, snow, rain, wind, sand. Supports a Nikon 400 2.8 VR G, TC, plus D5. Not a problem.

I second APS. They have repaired TWO of my older Nikon lenses. Fast, firm, quality work. Great customer support.

I use a Lowepro AW500 for my D4 attached to a Nikon 400 2.8 AFS G VR, plus other gear. Works great, fits travel size rules for most airlines, fits nicely. $150-200.

For three years, I have had great luck with Yongnuo. Manual: YN 560 III and IV are good choices. But the YN 660 ($75 on Amazon and Ali express) would be my pick. About the same price. Lots of great features, plus more output than the Nikon SB5000. Have used them on about 20 shoots and totally pleased. Pick up a YN 560 TX II wireless trigger ($42 Amazon) to run the YN 660 from you D500...$125-$130 total. I also have the YN968 N II. HSS and i TTL with Nikons (on camera). Excellent flash.

Nikon agreed to give me a new D610 for my near new d600 due to oil spots that they could not fix after TWO attempts. AND my D610 STILL had oil spots, monthly. I must have cleaned the sensor 50 times. Gave on the platform. Bought a used D800e for about $100 more than I paid for my D6xx and have never had a problem in two years. But, the D610 takes outstanding pictures. Good luck.

Ditto on Innorel RT 90c. After a field test along side an RRS (my first choice, totally amazing, BUT our of my price range) with similar specs. I have been using mine 2/3x a week for about a year, in all weather conditions. Super solid. Not a problem. Terrific fit and finish. I picked mine up during a Innorel sale along with a matched Innorel N44 Ball head for $328 total, delivered to my home in Hawaii. 3 year warranty.

The Yongnuo RF 605n set has been a real workhorse for me, both for OCF AND remote shutter release. I picked up 4 transceivers for $58 about a year ago on sale. Solid performance. The manual is beyond awful so you need to be willing to invest time in some trial and error. Yongnuo speedlights have worked out very well ( 1 year of regular use, "0" problems) for outdoor, sunset portrait work.

I needed a "global travel friendly" zoom lens, that could double for wildlife. Nikon's 80-400 was a candidate, along with the Sigma and Tamron offerings @ 100-400. I was able to field test both the Nikon and Sigma (could not get a copy of the Tamron). After a couple of days, 2000 +/- shots, the Sigma won out with a slight edge in IQ, weight. Nothing wrong with the Nikon, but for $1200 more...?? Very happy with the decision.

After about 4 years, very good experience with my Induro CLT 303. HOWEVER, if you can wait a bit for delivery AND you are willing to purchase something directly from China (NA on Amazon right now), you might want to check out Innorel. I needed a super duty T-pod for wildlife expeditions supporting my Nikon D4, flash, extender, and 400 2.8 VR nikkor lens in extreme weather. Budget approval from my spouse for Gitzo or RRS was not happening. BUT a recommendation from a trusted source led me to the RT90c with a M52 ball head. On sale end of last year, $328 including shipping and tax. (Note: I use a Wimberely Gimbal on the RT90c, not their ball head). Excellent fit and finish. After 6 months of weekly use, in all types of weather and high wind, highly recommend. The ball head feels/looks/machined like the RRS BH 55. But in as much as it has not seen a lot of action yet, the jury is still out on the Innorel M 52.