Keeping in mind that this server appears to implement only a tiny subset of the features the ones it is benchmarked against do... No lighting, mob spawning, mob ai, redstone functionality, tree or plant growth, water/lava flow, etc.

These wouldn’t significantly affect the first 10 chunks loaded?

More than a "yes, it should". While loading chunks you need to take redstone, nature and mobs into account. If you don’t - you need to find them and resolve at runtime with even bigger costs, relying solely on difference between programming languages in performance.

Yes but also consider the extensibility accessibility Java gave us. EVERYONE was building Minecraft mods back in the beta days. I might go as far as to say that extensibility is what made Minecraft so great.

What I always found surprising was how many minecraft mods there were despite mojang having absolutely no mod support for the game.

After learning that to make a minecraft mod the process was basically decompile minecraft fight the terrible names provided by the decompiler to make your changes then recompile it, I lost all interest.

Yarn[1] has pretty much fixed this along with fabric.

[1] https://github.com/FabricMC/yarn

No doubt about it. I don't think Minecraft would have gotten as far as fast in the public consciousness without content creators like Yogscast being able to produce so much novel content from modded Minecraft.

I was suprised myself thats its that bad. Well optimized binary is that what your CPU loves not a big JVM runtime