Aye, full auto's only good if you're fighting in an elevator. You could change, say, the Assault Rifle's burst option to only fire 3 shots and balance the AP a little more, problem is that would make the overkill animations look positively daft.
OR, you could give it one burst option that fires 3 bullets and another that fires 9, but then there's the problem of having no single shot possibility.
But here we are again with the realism versus fun debate, and I should mention that I for one do love being a cowboy and bursting like crazy. It's up to what people want to have in their game, really.