Jetbrains (PyCharm and RustRover) for projects; Sublime for one-off files.

The last time I checked out Jetbrains' IDEs, they felt heavy as hell to use. Has that changed?

Yeah, JetBrains IDEs are Java-based, so rather heavyweight. Then again, VS Code (and Cursor) have a browser engine running in the background, so not really better in my book. Sublime and Zed are more efficient of course. OTOH, JetBrains IDEs might be memory intensive, but don't actually feel sluggish on my 5 year old Core i7 laptop with 16 GB RAM.

Visual studio (at least its "core") is written in C++, yet is very heavy weight, so it's not the programming language at play here.

No. Still heavy as hell. (AKA uses loads of ram and CPU, slow, sometimes unresponsive). It is the price we pay - the tradeoff is IMO the unmatched editing and introspection/refactoring capabilities. I'm surprised there hasn't been a real competitor in this space.

I've been running a latest-1 version of a few of their products on silicon Macs since M1 w/ 8GB RAM without issue. I use minimal plugins and work on medium-sized codebases and their IDEs are some of the most reliable software I use.