Well (Ok, I'm partly contradicting the article here), most of the things LSP supports (autocomplete, jump to definition, ...) have been pretty standard features of more advanced IDEs (the original Visual Studio, the various JetBrains IDEs, even good ol' Delphi) for decades now. So the "problem domain" is pretty well defined already, LSP is just standardizing the interfaces.
Advanced IDEs are advanced because they provide so much more beyond basic jump to definition and autocomplete (which, again, can be very advanced and be context-aware, provide code shortcuts etc.).
It's good that tooling has improved across the board for many languages with LSP, but there's so much more still.
