The problem with Apple iGPUs is that when you try to game on them they aren’t as effective, mostly due to memory. And when you even make an MCM with a GPU tile next to the CPU and design a simpler interconnect it will still have the problem of cannibalizing heat of each other and then memory.
Integrated 780M with current top 7500MT/s LPDDR5x can get relatively high scores in GPU synthetic tests (at least some of them) but in games, it can start losing to basic dGPU much more significantly.
We had Kaby Lake G with HBM VRAM which solves the VRAM limitations but still left the heat issue and at that time it was just slightly better than the dGPU Nvidia counterpart it competed against.
And look at the Asus ROG Flow Z13 tablet with like RTX 4050 - when gaming the CPU will pull a fraction of power and will be away from the GPU, boosting high on one of the very few cores used by the game. Heat could hamper that essential boost.
LTT just released their video doing their own mod… coincidence? :)