Well, Minecraft is notoriously slow, but I guess that's very much nothing to do with Java, but the un-optimized code... Have seen quite some developers criticizing Mojang for this.
Although, maybe it doesn't count as I used mods like Optifine, which are made to ... replace said un-optimized code, but I thought it was a good showing for Minecraft and the JVM anyway.
But it can overwhelm itself. There's a equipment called Elytra you can wear to slide down the air, and if you use Rocket when sliding, you gain a huge momentum boost.
If you keep boosting on a server, being fast enough to challenge the serverside world-loading, you can crash the server.
Another big defect is it's rendering is deeply tied to cpu time, and the game itself has limitation. My recent experience with a 200+ mods & shader setup is that with RTX3080TI (also better cpu) and GTX980TI it runs at same fps (20~30).
You guess right. There are some few fan made mods (optifine, sodium/etc) that often improve performance by an order of magnitude, from tens of frames a second to hundreds.
It's a shame for Java since the increase in render distance makes the game much more immersive.