Definition of gaming o Metal mobile vs OpenGL desktop is very different. Unless game devs starts massively porting their desktop games to Metal API for some reason I would say it's incomparable. Just like how CUDA doesn't exist on a Mac and AMD at all it's completely incomparable to any Mac vs Windows/Linux argument.
Game devs have started to massively port their desktop games to Metal a good while ago. Any unity games runs Metal natively. Virtually all games that were out for Mac in last two years run on Metal. Civ 6, Total War series, Larian games. World of Warcraft has been running on Metal since 2016. Even some relatively obscure indie games like 7 days to die are working on Metal support.
Targeting Metal these days is really easy. If you use a third-party engine (like Unity or Unreal), you are already set. If you are using your own engine and use Vulcan for cross-platform support, you are already set (MoltenVK). Only if you want to get more out of Apple GPUs do you have to get your hands dirty with manually implementing your engine around Metal — and given how fast M1 is, I have a suspicion that more and more devs will come to play with it, it's also a lot of fun! TBDR is a very interesting paradigm to work with and it make implementing a lot of interesting rendering techniques elegantly simple.