If you mean they have to solve the same problems with very careful design and programming, yes. It's non trivial. Even Postrgres had a correctness issue around

If you mean they have to solve the same problems with very careful design and programming, yes. It's non trivial. Even Postrgres had a correctness issue around fsync for nearly twenty years. If you roll your own, that's very hard to get right. I wouldn't have confidence in such a system that I've built myself.