I haven't gotten to try a mirror yet since I don't 7* until tomorrow. If I face an SA line up, I find Thrawn to be the better counter. Not 100%, but still pretty good. A lot of the videos show bringing in TIE Defender then Inq TIE. I would disagree on second reenforcement. I bring in Imp Shuttle so you can hopefully mark one of your TIE's that have forsight.
If ST TIE is in the starting three, I go with Profundity with Biggs as my only reenforcement. He gets obliterated pretty quickly, but it allowed me enough time to get to ultimate and win with even a five on three match up with my ywing isolated. I did get lucky and the AI brought in Imp Shuttle instead of the insta kill ship second.