This is simply not my experience. For example, an IDE lets you rename a variable or type in a semantic fashion, making it easier for me to iterate on names and land on something that people understand.

There's a huge mental component to coding (I doubt it's 90% though). In any case, an IDE makes that easier by getting the boring physical stuff out of the way quicker.

And the speed at which you write code is quite meaningful. I can easily write 1000 lines of high-quality Rust code on a good day with just the LSP (rust-analyzer) for support. More recently, I started a project that hit some bugs in rust-analyzer -- working on it was a comparatively miserable experience.

Edit: Never mind, I see above that you're comparing a full-fledged IDE to just using an LSP. I consider LSP to be in the IDE category; I agree that LSP is just about where I want to be and that a full JetBrains-like IDE is overkill. What I don't like is not having any sort of code completion or rename support.