Canon image quality/rendering
You can get them to look close, but there are small things that don't match up, Canon has very different kind of noise from Nikon for example, I find Canon noise pleasant whereas Nikon noise leaves me cold. Probably not a big deal (or even noteworthy) from some, just something I pay attention to in addition to all the other things.
You're right, and I would have gone Nikon if I wasn't also interested in the video capabilities of Canon. We each make our own compromises I don't mind adapters, but I use native mount whenever I can, and native lenses whenever they're better than third party lenses. There are some great Canon lenses, but the truth is some third party lenses can beat some Canon lenses but L and non. But I agree, it's all about the lenses, the other stuff is secondary. Lenses are the thing that affects image rendering the most, the first step. Everything the camera does is just manipulate the light that came through the lens, it's the lens that shapes it in the first place.