I suspect M1X’s excellent memory bandwidth is related to the lack of replaceable memory. x86 CPUs can, as far as I know, max out the bandwidth of their DIMMs, and they don’t get anywhere near the bandwidth of M1X. And integrated design can do better.

Complaining about the price of Apple’s RAM seems reasonable, but complaining that they didn’t choose DDR5 DIMMs when they appear to have chosen something better seems silly.