The mini has a 65w tdp cpu, vs the mbp’s 45w cpu. That means more heat to dump from a smaller surface area. I’m not surprised they couldn’t fit a warmer gpu in the thermal profile.

Yea, it could at least have been an option. But my guess is they didn't want too many SKUs, and wanted to hit a price-point of less than $1000.

Also they need to preserve a market for the "modular" Mac Pro next year