If you look at all sorts of limitations on the M1 macs (less ports, only one external screen except on Mini where its one DP and one HDMI) it's plain that it's paying the price for using a phone SoC in a general purpose computer - no generic expansion buses, connectors optimised for phone use case, etc.

And they are banking hard on unified memory model in all sorts of marketing zbut it's unclear if it's the cause or effect of ring unable to use external GPU.