I'm not moving the bar. I didn't set it to where they were not going to eliminate some along the way. So this isn't a big "change" from my position at all. Nor have I 'moved the bar" in some sense that iGPU are necessarily limited to always being slower than dGPUs. However,
There is exceedingly little evidence though that Apple wants to put in multiple, broad range of Metal family targets into Metal. There are zero dGPUs supported now in macOS 11. Not even Apple's GPU. Apple is out to be "king of iGPU" implementing. That's nice and will lead to a decrease in the number of dGPU they buy. But that has some inherent limits on scaling. Folks who throw 8-10 billion more transistors at the problem than Apple does have a pretty good chance of going faster on a decent variety of workloads. ( especially in the generalized computational space. )
The top 500 supercomputers in the world (
https://top500.org/lists/top500/list/2020/11/) . in the top 50 how many pure shared memory systems in that list? None. ( probably none in the whole list but don't feel like walking through the whole thing to verify.)
And dGPU also doesn't necessarily mean can't cut down on the amount of copying.
Smart Access Memory will work on Intel, AMD combos too.
www.tomshardware.com
Apple has been lame on covering those elemnts from OpenCL 2+ for years and following the base infrastructure that is in the lastest bleeeding edge dGPU packages. That doesn't mean it isn't out there. Just means that under the narrow subset of limited macOS drivers they have an edge. That's lack of doing the work. not hardware.
Sure If Apple remains slack and behind the curve on implementing PCI-e v4 , v5 , 6 ( and CCIX and/or CXL ) they will paint Macs into a corner where Apple iGPU is the only solution, but that isn't necessary nor absent of being dubious on Apple's part.
Does Apple have a better iGPU in the wings. Sure. Is Apple going to whip AMD MI100 and Nvidia's A100 implementations in a computational drag race over the next two years, probably not. Is Apple going to whip a pair of those in a system over the next three years.... even more probably not.