In that case something dramatic is eclipsing it, it should be noticeable. It may be the GC threshold. There's about 5 settings recommended for perf issues.
Ordinarily I'd ignore rabbit holes like this but LSP is unusually useful. It's worth a shot.
I've done all of that. Still slow. I think the problem is other people have lower standards than I do when it comes to speed.
There's a command called M-x lsp-doctor that will tell you if you meet all the performance requirements for LSP mode. Among those is emacs 27 compiled with native json support (you can build emacs 27 without native json).