Intellisense dies when you write heavily templated C++ code (and there are valid production cases for that: in my job we write lots of expression templates to produce optimized math code). In contrast, I found clangd to be pretty responsive even in such scenarios.

I thought that was just their term for code aware features like jumping to defn/references, doc popups, completions, renaming and so on. That is in no way unique to vscode.