I wouldn't really count the Gozanti and TIEs as part of the fleet that the Phoenix cell has. Star Wars, in defiance of all logic concerning insurgencies, seems to ignore the idea that a rebellion would primarily use material stolen from the group its rebelling against and instead insists that the two sides be visually distinct. So even though it makes total sense that the rebellion would be lousy with TIEs and Gozantis and stormtrooper armor for their soldiers and primarily use stolen tech, instead you get each side using radically different equipment (except for the occasional, one-off infiltration story. Which means that there was never any chance that the phoenix cell would actually USE their stolen ships on any sort of regular basis.
Well, I think they don't use that stuff because it draws extra attention.
Flying civilian vessels, you can try to fake actually being civilians.
If you're flying around in stolen Imperial vessels without current clearance codes, it's a hell of a lot harder to try and explain that you aren't rebels.
Also, after what they did with the stolen TIE, I'm confident that the writers are holding on to that stuff. Ezra has already been shown to collect military hardware, so the notion that they might be building up a collection of garishly painted TIEs, and a ship to carry them, amuses me.
Edited by DarthEnderX