This is one thing I am concerned about. Apple keep talking about shared memory in relation to the ARM Macs. I hope it's not the death of dedicated GPU's in the Mac.
I agree on the CPU side, Intel is doing quite poorly. Not reaching their targets, taking too long to develop new chips and processes etc etc. However as you correctly have said, AMD and NVIDIA are moving ahead pretty well. Probably in part bacause they keep trying to one up each other. Proving that competition existing is a good thing.
If the ARM Macs are all integrated GPU's then It's up to Apple to prove to us how they are supposed to be able to compete with AMD and NVIDIA. I don't think any i-GPU can compete with that. The technology is not there yet.
Also Apple's language has been focused around better performance per watt of power used. This goes against the cutting edge offerings from AMD and NVIDIA which are beastly GPUs that don't care how much power they consume.
This is a bigger issue than some arewilling to admit. Why? Many Mac owners buy their Macs because they are decently usable for a long time. People still using 10+ year old Macs is a thing. I'm almost there myself with my 2011 iMac. Gatting a relatively decent dedicated GPU in your iMac means in 8-10 years time it'll still be decent enough to do most things. I don't know how well integrated graphics options from 10 years ago perform today.
Apple have proven they can design good CPUs thanks to the iOS devices. But GPUs? Apple hasn't designed any dedicated GPUs as far as I know. All their offerings seem to be ingetrated. We'll know the answer before the end of the year though as Apple has said they will ship at least something ARM Mac related before the end of the year.