Heck I was still using my 2012 Macbook Air until pretty recently, a decent machine if you don't mind that it gets really hot under load.

Barring any major fiascos (like past keyboard issues), the 2021 MBP does look built to last. We're in a good spot now in terms of stuff like a great screen (if you don't need constant 120Hz), low-power video decoding, a solid 8-core CPU, and probably even a passable gaming GPU. Should remain very usable even as it's outclassed in subsequent generations.