Because i would use the panzer III, and I wouldn't use the centurion, same way I haven't really used the Tiger II. I have more than enough perks for it, it would easily let me get my k/d up off the deck, but thats not what I'm going for.
As to the IAR-80 speed, thats was actually the IAR-81C, I think. The bombrack caused significant penalties in speed, climb, and acceleration. And even if it is correct, its still not much or any worse than the Hurricane, 109E, A6M, Brewster, I-16, and a couple others.