Arguably what's an appropriate GPU bandwidth is largely defined by the display attached to it, primarily its resolution, color depth, and refresh rate.

But I still don't think it makes sense to physically merge the two.

Displays wear out far faster than the GPUs driving them, and just have much higher failure rates in general, being physical targets for thrown handheld controllers and what not. Doesn't seem wise to make the display so much more costly to replace by shoving the GPU within it.

But this is Apple... making this expensive to replace is kind of their M.O.