When has an APU ever been as fast as a GPU? How much cache does it have, a few hundred megabytes? That can't possibly be enough for matmul, no matter how much slow DDR4/5 is technically addressable.
Ryzen5 has both CPU+GPU on one chip, the BIOS allows you set the amount of VRAM. They share the same RAM bank, you can set 16GB of VRAM and 16GB for the OS if you use a 32GB RAM bank.
What I'm saying is that GPUs rely on having the memory close to the die so that it actually has enough bandwidth to saturate the cores. System memory is not very close to the CPU (compared to GPUs), so I have doubts about whether an APU would be able to reach GPU levels of performance over gigabytes of model weights.
