Yes, you are absolutely right! That was also bugging me.
A few days ago I saw a comment by Richard Feldman on reddit (https://www.reddit.com/r/elm/comments/5jd2xn/how_to_structure_elm_with_multiple_models/) where he addresses the more general problem of scaling the architecture of an Elm app. His advice for when the `Msg` gets too big is basically the one you just described, so I think you’re right on!
Actually, I think his whole comment should be on the Elm docs :)