The last issue is that Republic ships can shunt power over to shields in an emergency, pulling power from weapons and boost to add shield strength. Whatever damage you take, is what you get. TIEs have no equivalent recharging health system. It is also possible to add shields beyond the max standard rating by overcharging them, giving them even more health.
And surprisingly quickly if you put full power to shields.
First, and most obviously, shields recharge. The other 2 issues are related to the function of the shields themselves. The DPS of the TIE doesn't overcome the effective health of the Republic ship. Straight up, put a Republic and Imperial ship of the same class head-to-head, and the Republic ship will kill the Imperial ship every time. The combined health and shield ratings of Republic ships far outweigh the relatively small increase in damage for Imperial ships. There are 3 fundamental issues here which make Republic ships just plain superior. Xwing: standard: 450.1 dps, 7.5 shots/sec - 4 cannons Tie Fighter: standard: 480 dps, 6.7 shots/sec - 2 cannons