Just personal preference. I like both, actually, I think the only difference between them is basically the tools you create them with and the scope of them. You can use models as level parts just as well, and with some more specialized processing they suddenly become maps...
Quite some of the things you mention aren't really true, bytheway.
No specialization in mapping? How about the design part, lighting, architecture, art (after all, creating textures is for mapping what skinning is for modelling)?
Mapping all done by yourself? Reality is quite different in the bigger companies. Often multiple persons work on a single map in sequence.
No modelling limits? Sure are. Just as with mapping, this depends on the engine you're using.
You can request maps. There's people being paid for mapping.
So, in the end, I don't see a reason to fight, having experience with both.