On the IDE marketshare question, the Stackoverflow Developer Survey asks questions like this and I always jump to that section. Here's my comment on HN summarizing the most recent survey https://news.ycombinator.com/item?id=44725015
I also wrote about VS Code's early rising with a focus on marketshare here https://blog.robenkleene.com/2020/09/21/the-era-of-visual-st...
I also think your observation about VS Code's rise forcing JetBrains into a corner is spot on.
On a side tangent, I find it odd that the whole VS Code phenomena is under analyzed. Before VS Code, text editors and IDEs were one of the healthiest software categories around, with the market leader hovering around 35%, which is great for competition enforcing quality (DAWs are still like this today). Now text editors have become more like the Adobe suite, where there's in 800 lb gorilla doing whatever it wants and everyone else is competing over scraps (if you say VS Code is actually good though, Photoshop was amazing when it made its rise too). Developers just let this happen to their core tool without anyone really talking about?
I honestly don't understand the popularity of VS Code, at all. If I wanted to cobble together a development environment from scratch, I'd just go use Emacs. Hell, I'd end up with a better product than a bunch of buggy as VS Code plugins that don't constantly act up and regularly break.
While I wouldn't consider my employer a '.Net shop' anymore, it's a fact that it still remains the most used language across the organization. Many of my coworkers have ditched Visual Studio, jumped to VS Code, gotten pissed off at it after a while, tried Rider, and eventually switched.
If anything, I think VS Code is in an incredibly unhealthy state. Sure, Microsoft initially managed to pull a Chrome with it and ate the lunch of a lot of more basic text editors, but many people are getting frustrated with the ecosystem. Really, between Spacemacs and Neovim, actual community-driven projects are coming out with much more polished and better integrated tools than Microsoft - partly thanks to them pushing everyone and their dog to build language servers. I'm sticking to proper IDE's for basically everything but the occasional itch I have to do something in lisp, but hot damn does what you get out of the box thanks to LSP support and tree-sitter make VS Code less appealing to people willing to make the switch.