No player can win matches alone, the gulf between England and Australia/India in their home turf in the prior decade or so has frankly been huge, you can't expect him to lead us to victories when the rest of the team simply gets completely rolled.
Stokes last two years hasn't bowled much at all but again, the fact remains that he is an all rounder who can be called upon when the need arises, but with the three pacer and one spinner system actually working he hasn't had the need to bowl too much which is good because he has had knee surgeries, that doesn't change the fact that he is still a pacer good enough to average 29-30 with a 55 strike rate whenever the need be, you add that with him being a clutch batsmen and you got a better cricketer than Pietersen.
I don't know why you're mentioning Dev, as if he wasn't suffering from multiple factors effecting his stats, and as if he wasn't a better bowler than his average suggests, but no, Stokes isn't a Dev level bowler, longetivity, workload and so forth.
and tbh, 36 average isn't that bad in this era, that would be equivalent to 40 probably in 2000s aka the era KP played in, and No he doesn't need to average 50 lol, KP and Cook are not in the same league as Root, don't mention them with him.