You are correct, it is not a lightening fast focusing lens, it takes about a second to focus, but, it's used for portraits and is arguably the best portrait lens Canon has ever made. The 85 f/1.8 is a good lens and for someone who's budget prohibits purchasing an 85 f/1.2L, either the original, which I have, or version II, it will do the job and do it well.
The OP did say best portrait lens for Canon.
There are two lenses I mainly use for portraits. On crop bodies I use my EF 28-70 F/2.8L. On Full Frame bodies I use my EF 85 f/1.2L. It's big, takes it's time focusing, and produces the creamiest, smoothest, most complimentary and most bokehlicious portraits of any lens I've ever had the pleasure of using.
People knock the 85 f/1.2L because it doesn't focus fast. It's a portrait lens not a sports lens. The small amount of time it takes to focus is irrelevant, plus, if you know what you're doing you'd have pre-focused anyway and would be using manual focus. The portrait subject(s) are posing. Do you think they can hold still for a few seconds!? I've even used it for infants, I have 6 grandchildren, with spectacular results. There is something magical about that lens that makes it ideal for portraits.
If the OP doesn't want to spend money on some exotic or specialty lens, the lens she already has will work quite well.

The 50 mm lens for portrait work always generates interesting opinions. In fact, I have seen virtually word riots on both sides endorsing the lens or vehemently dismissing it's use for close up work. For 1/2 to 3/4 length most agree it's a good match on a crop or full frame camera.

Crop sensor cameras are always the source of fuel for these lively discussions within that focal length. I don't have a clear cut answer for those working within shorter focal lengths other than choosing longer than 50mm. Unfortunately, in tight quarters, you run out of room and the relationship with the photographer and subject is reduced to a long distance phone call using a crop camera and focal lengths 85 mm and above.

Frequently, I've seen Joel Grimes used lenses like the 24-70 almost within minimum focusing distance with minimal distortion. That man knows just the right plane to reduce the exaggerations of body parts.

Here's one photographer who rejects the 50 mm as a portrait lens almost in war-like fashion. I'm not patronizing either side of the camp. Just another perspective to be shared for those interested. I generally use a 85, 100, 135 or a 70-200 but that's on a full frame.

https://www.youtube.com/watch?v=nG1pN5Vic8E

You are correct, it is not a lightening fast focusing lens, it takes about a second to focus, but, it's used for portraits and is arguably the best portrait lens Canon has ever made. The 85 f/1.8 is a good lens and for someone who's budget prohibits purchasing an 85 f/1.2L, either the original, which I have, or version II, it will do the job and do it well.
The OP did say best portrait lens for Canon.
There are two lenses I mainly use for portraits. On crop bodies I use my EF 28-70 F/2.8L. On Full Frame bodies I use my EF 85 f/1.2L. It's big, takes it's time focusing, and produces the creamiest, smoothest, most complimentary and most bokehlicious portraits of any lens I've ever had the pleasure of using.
People knock the 85 f/1.2L because it doesn't focus fast. It's a portrait lens not a sports lens. The small amount of time it takes to focus is irrelevant, plus, if you know what you're doing you'd have pre-focused anyway and would be using manual focus. The portrait subject(s) are posing. Do you think they can hold still for a few seconds!? I've even used it for infants, I have 6 grandchildren, with spectacular results. There is something magical about that lens that makes it ideal for portraits.
If the OP doesn't want to spend money on some exotic or specialty lens, the lens she already has will work quite well.

He's not the only person that has NOT recommended the 50 mm. You are welcome to your own opinion of course. I merely included the link as a point of interest and not a judgment. Eariler I referred to Joel Grimes using a 24-70 2.8L II at 24 mm at MFD with minimal distortion. It's really up to the person buying to make the decision through many viewpoints. I personally don't use a 50 for portrait. I prefer longer focal lengths. That's a personal choice.

For what it's worth Cazillo partnered with FroKnowsPhoto for a while. They split a number of years ago and went their own way and no, I don't watch the Fro at all. He's on my blocked YT list.

He's not the only person that has NOT recommended the 50 mm. You are welcome to your own opinion of course. I merely included the link as a point of interest and not a judgment. Eariler I referred to Joel Grimes using a 24-70 2.8L II at 24 mm at MFD with minimal distortion. It's really up to the person buying to make the decision through many viewpoints. I personally don't use a 50 for portrait. I prefer longer focal lengths. That's a personal choice.

For what it's worth Cazillo partnered with FroKnowsPhoto for a while. They split a number of years ago and went their own way and no, I don't watch the Fro at all. He's on my blocked YT list.