Levitate wasn't broken, the AI was just not programmed to respond to it. I can think of several things off the top of my head that could help balance the AI with respect to tactical spells (for this, tactical spells means a spell that improves your situation tactically without dealing direct damage):
1. Use the right tool for the job.
- If levitating use something ranged, or dispel.
- If invisible use area effect, or dispel.
2. Use the terrain.
- If levitating try to find somewhere that the floater can't get a vantage point on you, or break line of sight.
- If invisible find water or high grass, find an area that minimizes approach directions.
3. RUN!!!
- For either, if none of the above are available to you, RUN AWAY! It's what I would do. . .You could run to a location that is better suited, or find some buddies that are more equipped for that situation.
I think tactical spells are fun, and would be very disappointed if too many are removed in favor of direct damage spells. I had a lot of fun in my Telvanni stronghold in Morrowind, and having to levitate into the inner chambers really added to the ambiance and made me want to spend more time there.
I hope they leave spatially triggered events in Call of Duty games, and don't rely on them too much here. I also hope they don't pour ALL of their resources into making it a combat-centric game. While focusing on the fighting is good since there is a bit of it in there, for me it's the non-combat activities (and spells) that keep me coming back to a game like this.