Writing high performance Java is definitely a bit of a dark science, a lot of the performance isn't just the code loop you're looking at, but memory allocations matter quite a lot as well. Complex hierarchies of large long lived objects can absolutely tank your performance.

There can also be a lot of performance to be gained by going off heap. I'd be probably be looking at an ECS design around MemorySegments, rather than modelling the game state with Java objects. Though, to be fair, this is how you'd write a game engine in C++ as well.