That's only true if you're using X-wing Alliance numbers rather than the TIE Fighter stats, DScipio. If we go the later then the Avenger gets lightly toasted.
TIE Avenger: TIE-Defender:
Speed 145 MGLT 155 MGLT
Manuverability 150 DPF 175 DPF
Shields 100 SBD 200 SBD
Hull 20 Ru 20 Ru
Hyperdrive Yes Yes
Laser 4 4
Ion - 2
Warhead Capacity 4 Capacity 4
Tractor Optional Optional
Trying to see if I can find a source for their other statistics, but I'm not sure there was one at that point. Either way, the Defender was 'broken' there, was omitted in X-wing vs. Tie fighter for that reason (The game file does exist, and it apparently reads "Advanced space superiority fighter. This craft is too powerful to be put in this simulation. Dream on, fanboy!"), and reintroduced in Alliance with toned down stats.
Edit: corrected by source:
Thanks, as I could not find the TIE-Fighter stats. However even in TIE-Fighter it was more satifing to down TIE-Defender (traitros) with the Avenger than the other way around.
I also always thought that the TIE-Defender was a good concept for a rare Elite-Fighterbomber, while the Assualt Gunaboat and the TIE-Avenger were more plausible as actually mass-produced fighters (altough not in the scale of the T/F, T/I or T/B).