This is the sort of thing that makes me reconsider using Jetbrains at all, even though I prefer it to VScode. Enshittification rarely reverses once it starts...
Not that I really disagree with the premise though. IntelliJ has not gotten any better with every update for a few years, but it does get slower and slower.
Jetbrains in general is really poor at dealing with user feedback. My pet issue (showing the path in search results and tabs, so you don't just have a bunch of index.js files that you can't tell apart) has been ignored for years despite consistent votes and comments.
Hm. I didn't know there was an installed-per-default assistant. Maybe it's disabled if your workplace uses Copilot?
I use Rider, WebStorm, Datagrip, CLion (and occasionally Android Studio) and haven't had this thing thrown in my face yet. The "new UI" can go diaf though.
It unfortunately doesn’t appear that it is. I downgraded my Jetbrains IDEs because AI Assistant kept trying to clobber over my other tools, even when disabled.