They're not, but you're limited in what you can do. Violin is great, but how about some cello and piano?
Again, I don't feel that these are the sorts of limitations, but rather a fair comparison would be being forced to use at least piano, Cello, and violins rather than having the choice of only using violins.
Using a real world framework doesn't force you to do less, it only forces you to have certain elements in your map, which as I've already pointed out isn't a bad thing.
Not in my experience, since there's no way you could screw things up (I used to be an avid mapmaker for a different game, Heroes 3 of Might and Mage).
It's much easier to just draw some crazy shapes that simply don't work for warlight games when you're working completely from your imagination. Sure, it's possible to have a better map, but it's also possible to have a really, really bad map if you just draw it yourself.