IIRC, compared to GPUs, M-series is currently still stuck in memory bandwidths from around 2016. M7 might catch up to 2019 or so. So GPUs will be better for LLMs for a pretty decent while.

How so? I don't know of any other mainstream platform with >1TB/s memory bandwidth. Personally I don't want to deal with macOS but between the memory bandwidth and out of box Thunderbolt networking it's hard to argue that Apple doesn't have a couple significant advantages over the current alternatives.