Well, splitting into large maps is not itself a bad thing, as long as you can freely move back to previous maps regardless of where you are in the story. My preference is that maps should have content of mixed difficulty to avoid a linear feel, although I know that does not always work.
I thought that the Witcher 3 managed it quite well having several large maps with some general difficulty progression going between them as the story progressed, and giving fairly clear guidance through the journal when a given story/quest path was likely to be an inappropriate level. There are probably many other ways to indicate encounter CR if putting it directly in the journal is considered a bit blunt.
Not that getting into overly difficult situations should be as common if the level range is only up to 10.
