The A18 Pro is going to out perform many "decades old" processors, which would you be referring to?
I wouldn't conflate "affordable" with "low-end" in terms of processing speed. Apple is able to get the price to this point because of decisions that the rest of the market did not make.
I'd agree that an m1 chip can probably continue to run modern macOS for a very long time, and they will likely drop support for it much earlier than they would need to.
I understand that running for power users and running for my uncle aren’t the same.