That’s the pain point - well written java code may not be the most performant depending on the situation.

It wasn’t just optional but other areas as well.

That's not my experience, though game development is certainly a niche and Java may not be the top choice for that.

You might sometimes have to reach for SoA-like structures and reference them via indices, at least for the core ECS, but for the rest you can easily use bog-standard Java -- not everything has to be "ultra-fast, specially written java", just certain hot loops.

Right. I didn’t started digging into it until I realized the application was clearly sluggish in certain scenarios. As I am doing this for fun I am going to see what kind of speed up I get in rust for this.