Have you profiled things and have data to show JSON handling is the root of the performance issues?
Further details...
... from the same source as the top post: https://www.masteringemacs.org/article/speed-up-emacs-libjan...
... from lsp-mode: https://emacs-lsp.github.io/lsp-mode/page/performance/#json-...
It's Emacs needing to be configured to use faster JSON libraries.
The original comment was complaining about JSON as a format itself, and my argument is that unless you need super high performance, JSON is more than enough. And it's not like LSP is passing around GB of data every second, let's be real here :-)