By that definition, I could just as easily argue that requiring different files for every class reduces cohesion. The idea that class definitions and file definitions are in any way related is a leaky abstraction.
I've never been a fan of the class-file coupling. It pulls me out of the mental model I'm trying to build in my head and forces me to think about file organization which is almost always inconsistent with the language semantics I'm dealing with.
I've used IDE's that make this more or less painful, but none that actually solved it. If anyone has any suggestions on one that does, I'd be interested to try it out. I don't really care what language. I can pick up enough to see what it feels like.
I also want to say that rich hickey talked about a file as a unit of code not being very good, but I don't recall where, or if he really said it. I want to say it was in a Datomic podcast right around when details about it were coming out.
