I suspect the M2 (non pro/max) will continue occupying the £699 slot for the base config. The M2 is likely to be a small spec bump, so the M1 Pro will remain more performant. I don't imagine the M2 Pro/Max being released until 2023 or very late this year.
I think (hope) you're right. Desktop components tend to be cheaper as they have less constrained power requirements/tolerances. This goes for processors too, the M1 Pro/Max may be binned on power usages as well as functional components, Apple are subject to the same silicon lottery that is present in AMD and Intel chips.