the level designers absolutely had to model stuff because of the nature of the game (like they had to measure the distance between buildings in Dishonored to predict if a player can jump between them
That's not true - the tool that allows a designer to place a house model will usually have some sort of scale in there. It doesn't mean the level designers were modelling the houses. In fact, given that Dishonored has separate teams of level designers and level artists/architects in the credits it's extremely unlikely that level designers were doing the modelling.
Anyway, as you say, the production method depends a lot on the game, and this is why we don't have any standard terminology for designers in this industry. Certain types of game require (or at least benefit from having) level designers with some degree of modelling skills as the tools require them to sculpt or construct the play area, decide on its broad appearance, and so on. Other types of game will have a tool that is more about assembling pre-made objects and the designer here doesn't need to have any sort of modelling or artist skillset.
You say "I find it a little non-effective if different people would work on plans and on level design itself in 3D app or an editor" but others will find it inefficient if you expect one person to have all the skills from planning the level from a game design perspective right down to being able to manipulate the mesh and textures in a modelling tool. People have to play to their strengths, both individually and as a team.
Only the developers on a certain game can tell you exactly how they went about it. Even 2 games with the same engine might approach things differently, if one team is using a lot more prefabricated scenery than the other. The skills involved in level design may overlap with skills involved in environment art, but it all depends on how the team works, and what tools they use, and what sort of game they're making.