But I've just picked up TS2022 again, finally having a PC that can take it. I want a lean installation, ideally removing duplicate routes. But does removing a route DLC via steam remove its rolling stock too, and if so, is there a way to avoid this?
Depends on the specifics. If a rolling stock was shipped with the route, then yes. If it is a standalone DLC for the route, then you can still use it, of course in your own scenarios. You could cherry pick files, restoring whatever is needed after uninstalling the route, but you'd probably have to extract the AP files and fiddle a lot. Unlikely to worth the effort in my opinion.
It depends on the package. Most have the rolling stock bundled in with the route. Delete the route and the rolling stock goes to. A few packages have some of the rolling stock as a separate DLC. For example the Mittenwaldbahn package has the OBB2016 as a separate DLC, so deleting the route won't delete the 2016.
The track map for a route is stored in Content/Routes along with it's scenarios. Everything else that goes on that map in the way of buildings, scenery, track and trains are in Assets. If you were to delete a route from your Content Folder you would still keep everything else. You could use the trains elsewhere and you might be using the Buildings in a Freeware route. I purchased Feather River Canyon because a Freeware route uses some of it's assets. And I deleted the route folder as I won't be running it.
