What do you mean? What’s the dps difference between Ret and Rogues/Warriors?
Well, a lot. Ret if you absolute min max and get all the consumables possible and ignore buffing people then you might do 2/3 of the ST dps a Rogue or Warrior does. Those consumables will cost you many hundreds of gold each raid and take a few hours just to pick up. You also scale worse with gear than Rogues and Warriors so you’re behind them in gearing prio, at least you should be, with the exeption of 2h weapons.
Ret also has zero aoe/cleave which Warriors and Rogues both have.
For PvP Ret is quite good, you’re easily kited by mages and hunters but other than that you should have a fair fight with most other classes.
The main argument against ret is that holy is so strong. Why play a barely functional spec when you can play the best pvp healer and arguably best pve healer? Nobody wants to group with ret, but everyone wants to group with a paladin. Hell people will pay to get you in groups with them as a holy paladin!