Anand was pleased years ago to be offering Xbox One levels of GPU performance on a iPad.Shadow of the Tomb Raider running on that thing was mighty impressive.
I think the bigger question is if traditional PC gaming matters at all on Mac OS. Most the gamers I know that run a Mac primary have a gaming PC anyway OR *shudders* dual boot into Windows to actually let their GPU use modern graphics APIs and optimized drivers. That seems less and less likely to be an option.
The number of PC Apple devices is surely dwarfed many fold by the phones and ipads, so it seems like a small target in general.