Most (all?) LSP implementations are open source. If the same effort they put into reimplementing the compilers went into making better LSP-based solutions, LSP would run circles around custom plugins, because LSP has accurate data from the official compiler. However, I guess I know why they are not doing that: because that would benefit the competition as well.
And yeah, obviously Java story is definitely polished, but it has been under development for decades, and also Java is quite a limited language.
Actually, Microsoft's Python LSP for VS Code is proprietary[1] (as are some of their other extensions) whereas PyCharm Community Edition is open source[2].
What about other things external to the compiler like immediately recognising and mapping project configs and structures (for example, Spring, or Symfony, or...)?
Or things like "version X of the language introduces new things and we can automatically refactor your code to reflect the new ways of dealing with things"?
No, it doesn't read like that.
> sometimes hardly even works for a bunch of languages that other IDEs and editors work fine with.
LSP is as much a hit-and-miss. And it's definitely not polished, let's say, for Java.