In Oblivion I was a Witchhunter and loved it. I really enjoy bow and magic combined. Seems in Skyrim, Bethesda removed the possibility of doing magic while having a bow equipped. You have to change between Favourites and it seems very slow to change. In Oblivion it was flawless.

Has anyone else noticed this and is unhappy with the change?

It's not too bad on PC (even though the UI itself is terrible). I usually punch the enemy with the bow, then double-tap a hotkey to dual-wield Firebolt or something. Bows are not the ideal weapon to be carrying in close fighting anyway.

Try Conjuration rather than Destruction. If you really want to use Destruction you have to switch manually... as a Mage you have to switch manually for everything (as far as I know)... it just takes some time getting used to.