To be honest, I have to smile tiredly when I read comments like this.
I wrote "as far as I know", which of course excludes a personal test, since I'm not in the Nikon camp. 😉
Nevertheless, I also work with professionals who just told me about this combination. Which is why I wrote a feedback to the previous speaker (xtam667) about the Z9 and the 800mm, he was talked about.
If you compare the lenses, you will notice that the lens is slower in low light situations and the motor/motors are simply louder compared to the lenses I mentioned.
Especially compared to the 400mm 2.8, which should be indisputable. In poor lighting conditions, there is also focus hunting - you have certainly noticed that.
This can be determined easily and objectively.
I am also not one of the "Canon customers" for me it is performance and not the brand that counts, regardless of whether it is a lens or a camera.
So it's not just a question of personal preferences, as is so often the case here, but also of objectively measurable and thus ascertainable performance of the respective camera or lens.
Certainly we are arguing here on a very high performance level of camera and lens. Regardless, it would of course be nice if Canon could also offer something in this class at a similar price. I wouldn't call it "milking" what Canon does, at least not in the USA. Personally, I see value for money throughout in order. In Europe it looks different again - and no, it's certainly not due to the sales tax - Ultimately, however, it is a question of the size of the wallet and Canon's willingness to continue to fill its pockets.
Ergo, a subjective decision, similar to the assessment of whether a combination is judged to be fast or not quite as fast from a personal perspective.