After reading the Ultimate Visual Guides section on the TIE Striker, I'm really liking it more. It's basically like the Empire's A-10. The higher-ups don't want it because it is a dedicated atmospheric fighter that provides great ground support that relies heavily on Repulsors which allow the Ion engines to give better thrust performance. The higher it gets or into space it's performance drops significantly, though. It says the pilots love them and love the deal they get from slicing through an atmosphere.
Chris