I have that kind of fast, smooth experience with VS Code, too - but that is when I open my small hobby monorepo, or only when I don't leave it open all day. When I open a big work monorepo (250k files, maybe 10GB in size, or 200MB when you exclude all the node_modules and cache dirs, the slowness isn't instant but it becomes slow after "a while" — an hour, or two.
I do actually regularly benchmark it and test with no/minimal extensions, because I share responsibility for tooling for my team, but the fact that it takes an hour or two to repro makes that sort of too cumbersome to do. (We don't mandate using any specific editor, either, but most of my team uses VS Code so I am always trying to help solve pain points if I can.)
And its not just the file saves that become slow — it's anything, or seemingly so. Like building the auto-import suggestions, or jumping to the definition by ⌘-clicking a Symbol. Right after launch, its snappy. After 2-3 hours and a couple hundred files having been opened, it's click, wait, wait... jump.
Eventually, even typing will lag or stutter. Quitting and restarting it brings it back to snappy-ish for a while.
It is true that maybe we have some configuration that I don't change, so even with no or minimal extensions, there might be something about our setup triggers the problems. Like we have a few settings defined at the monorepo root. But very few.
"editor.formatOnSave": true,
"editor.codeActionsOnSave": {},
But before you think
aha! the formatter! know that I have tried every formatter under the sun over the past 5 years. (Because Prettier gave my team a lot of problems. Although we now use it again.)
We have a huge spelling dictionary. I regularly disable the spelling extension though, but what if there was an edge case bug where having more than 1000 entries in your "cSpell.words" caused a memory leak on every settings lookup, even when the extension wasn't running? I mean... it's software, anything is possible.
But I suspect it is the built-in support for TypeScript itself, and that yeah, as you work with a very large number of files it has to build out a model of the connections between apps and libs and that just causes everything to slow down.
But then, like I mentioned nothing else I've seen quite has the depth of TypeScript support. Or the core set of killer features (to us), which is mainly the remote/SSH stuff for offloading the actual dev env to some beefy machine down the hall (or across the globe).
To us, these things are worth just having to restart the app every few hours. It's kinda annoying, sure, but the feature set is truly fantastic.