We're actively working on improving the game on Switch (we've been doing so ever since the release and keep working on it still), so you can still expect some improvements.
However, the Switch is very limited (specially with Unity as a middleware) so if expect a comparable experience as with the PC or one of the bigger consoles, it's not gonna happen.
The current version has reduced a lot the crashes. They still happen from time to time but it's something we're actively trying to improve. The good thing in Temtem is that crashes don't make you lose anything (other than the loading times), since you reconnect right where you were.
In terms of FPS I think it works pretty well overall, we're happy on that front. The main problem is memory issues and that leads to longer loading times (which will always happen) and crashes from time to time if the memory consumption gets big enough.