I think we butted heads on this before, but the civilized debate is always fun with people with the same interest.
I give you that nVidia is objectively better ignoring cost (cost per frame generally tends to lean toward AMD but not always) but why do you feel it's better for Apple? And the iMac specifically?
Btw, I'm going to try to defend AMD although I feel it's a losing battle overall. However I'm not so sure when it comes to Apple specific use.
Why do I feel it's better for Apple?
I feel it's better for Apple because the cards are better. It's established that it is necessary to have a mobile GPU in the iMac instead of a full desktop GPU. That is something we have to live with.
The new GTX 1080m is essentially as powerful as the full desktop version, nvidia is a great company and they continually strive to make a great product. Their newest mobile cards are essentially as good as the desktop counterparts.
You take the M395 it is
massively outclassed by the 1080m or 1070m. However all 3 can fit in the iMac.
And before the argument is raised that the iMac is not a "gaming machine". It is true that there are two types of graphics cards workstation cards and consumer cards. Even though the 1080 is good for gaming it is still a consumer card just as the M395 is. So comparing the two is completely valid.
The M395 can be considered a gaming card too though only a mediocre (at best) one.
Middle of the range components are unacceptable in a $3k machine. Sadly, I need macOS and don't have a choice.