Trenchbroom is very good, but I still think, it's not the best possible map editor. It uses brush-based approach, which isn't the right way of designing maps for games in closed spaces (like Quake). Creating each room requires creating at least 6 brushes for its walls/floor/ceiling, which is way to much for such stuff. On the other hand Unreal Editor (for first Unreal and Unreal Tournament) supports creating rooms directly (as subtractive brushes), when two room primitive touch each other, they are automatically connected.
I tried both and both are interesting. Conceptually the brush approach seems more intuitive for some types of maps. Like making a few rooms that come out into an open space or some oddly shapped stuff like pyramid rooms, etc. I dunno, both are interesting and once you got used to the approach, the additive system works pretty well.
Back in the day I made a lot of Quake 3 and Unreal Tournament maps. The Unreal Editor was a lot buggier than Radiant but the workflow was far superior. You could bang out a floor plan quite fast with the subtractive approach. No caulk textures to deal with either (a special texture that the renderer ignored for the sides of the boxes used to create the walls that the player never sees).
I know nothing about this scene, but interested to know more. I remember hearing that Unreal Tournaments engine used this subtractive model internally so it is not strictly editor ux decision?
I don't know what Unreal Tournament did use internally, it's hard to investigate, since there is no (official) source code release for it. But I do know, that brush-based (additive) approach isn't strictly necessary for creating maps for Quake/Quake II/Quake III, it's technically possible to write a map compiler taking maps in some subtractive format. The reason why it's not done (or at least not common) is because it's not a trivial task and because existing infrastructure adds some friction.
Couldn't this be solved by "map compilation"? IIRC, Hammer etc. did something like that. Occluded faces were removed.