I seem to do this a lot - I’ll find a game whose setting I really like, but dislike the ruleset it uses, so I end up converting it over to the ruleset I prefer (usually Cypher System). I’ve learned that to some people, this is blasphemy of the highest order, which is surprising. I still do it, though. 😬
That depends. Sometimes the mechanics are kind of integral part of the setting. Those reflect some realities of the setting. But then, if the mechanics are too crunchy for me, I would be looking for “X with serial numbers filed off” hack of another system