The lifespan of a laptop is not tied to a replaceable battery - if you buy a new laptop because you have lost 20% battery capacity, then you are making an unsound financial decision.

A laptop does not really degrade much apart from cosmetic wear or physical damages - instead, what the same amount of money can get you changes, and at some point you feel like that cost has been amortized and that the gap between back then and now has increased enough to justify a new purchase. The only reason M1's would last longer in that regard would be stagnation on Apple's behalf.

Same with how the PC market had stagnated with minimal generational improvements until both Ryzen and M1 shook things up in interesting ways.