M1 uses the same Firestorm and Icestorm cores as the A14 SoC. M2 uses the same Avalanche and Blizzard cores as the A15. So one can argue about the importance of the differences, but they are clearly two different generations.

M1 pro, max, and ultra still have the same cores, just a different number of them. One would assume that M2 derivatives will be the same: different combinations of the same cores.

Microarchitecture.

Marketing?

That's what the M is for

It's possible it's nothing but marketing, but I didn't want to assume that without knowing what I'm talking about