I believe I have won only 1 game out of 7 with my x3 Defenders with Ion Cannons List and ironically enough that was when I didn't fire the Ion Cannons even once the entire game! On the flip side, that was when the ship was first previewed so perhaps I should revisit it and give it another try.
I am surprised that anyone was able to consistently ionize X-Wings as the rebels can move 1 forward while the T/D has only a 2 forward, you shouldn't you overshoot sooner or later?
That's why you need to come from multiple directions, you don't have to always ionize with same ship. But also keep in mind that the Delta is PS1, so you can bump it, he moves away, you shoot it in the back. Especially useful against B-Wing with their 1 agility, you don't mind as much your lack of action by bumping.