(https://i.imgur.com/Te9bRDy.png)
I think it wouldn't be too hard to add a second option to the context menu so this section would have:
* Show Track Count
* Show Album Count
A column heading of either "Tracks" or "Albums" could be displayed, which would also make it more discoverable that you can click to sort it.
This heading might need to be optional to avoid crowding the Column Browser heading row with text, either for narrow displays, layouts with lots of columns or just user preference for a cleaner look.
<Artist> ($Count(<Album>,<Artist>))
<Album Artist> ($Count(<Album>,<Album Artist>))