It was more like Minecraft code was horrible, than anything else.

Creating objects like crazy, range for in hot paths, not caring about data representation, chosen algorithms,....

JIT and GC were already doing heroic efforts.

Yet, it settled Notch for life, which is something to take into account in the usual question regarding which technical stack for games.

For sure. The tech only needs to be good enough to support the game design. For some games that means very high optimisation is needed, and for others it's enough that the screen can refresh before the user gets tired of waiting.

Minecraft 1.7.10, covered in mods, can run fantastic (300+ FPS) if Java 25 is used. That used to be impossible.

Yeah at the time it was bad. Now, it's a pretty nice codebase