Would the people who were buying the baseline 8GB model (presumably just for general computing/office work) care about the GPU being slightly slower, though?

I bet that the extreme lag when you run out of memory because you have an Electron app or two, several browser tabs and something like Excel is way more noticeable.

Hardly anyone is using Macs for gaming these days and almost anybody who does something GPU intense would need more than 16GB anyway.