> a lot of engineers stagnate after a few years

Stagnate is also a way of saying got good at the job.

I mean after a couple of years at a place an engineer might be the person that know the systems best in the whole world if they are no commodity. It takes year to gain the experience and inside out knowledge of a complex system.

To me it feels like I get a mental picture over a system after some time where I can smell where bugs comes from and very fast decide were functionality should be inserted. Up to that point things are just a hassle and then it clicks and becomes a breeze.

Then I switch jobs to get a pay raise and the grind begins again ...