[ragnese]

Yes and no. I'm using rust-analyzer as an example, but I also use other language servers and observe similar UI lags/stutters.

When it comes to memory, my point is precisely that we should count the language server in the total and not just the Emacs process. So, when some other IDE is using multiple GB of memory on my Rust project, we have to compare that to my Emacs + rust-analyzer memory usage because both of those processes are providing the features that other-IDE is providing.

However, Emacs is also still kind of laggy when using LSP, even though the actual LSP server lives in another process and communicates mostly asynchronously. My understanding is that there are still bottlenecks in Emacs that make this not truly async. But, even if my LSP server of choice is extremely slow, why should that affect my cursor movement or typing speed in my Emacs buffer? I can see why it would be technically difficult to make it NOT introduce some lag, but it shouldn't in principle.

I haven't used Visual Studio Code, but my understanding is that it is plenty responsive to typing and cursor movement, even while using rust-analyzer.