https://www.techpowerup.com/gpu-specs/?architecture=GCN+1.0&...
That being said, frankly I'm amazed at what most modern mobile GPUs are capable of and for most people who are casual gamers, that level of performance will be more than enough. What Apple will bring to the table will certainly be better than that, it's already better than Intel GPUs and they can still support 3rd party GPUs if necessary.
The demo they showed of Shadow of the Tomb Raider running at 1080p looked great for a game, AND it also looked awful if you compared it to the PC version on Ultra settings.
The whole presentation struck me as a big middle finger to Intel and just Intel.
I was actually a bit surprised they would break that kind of a demo out at WWDC -- I've seen that game not running in emulation and it was beautiful. That demo wasn't.
Looking at it without context however, it demonstrated the capability of the platform to run a AAA game without developer optimization/consideration.
And it demonstrates someone could make a stylized game similar to Fortnite.
And that was released in 2018. By the time Apple put out desktop class silcon in end of 2020, surely it will be significantly scaled up?