Corvettes are not OP by any means, in squad vs squad battles corvettes are by far the least played class cause the players will know how to play as a team, stay together and communicate. At that point corvettes just become free kills. But even in a 1 vs 1 situation with players of equal skill there are so many counters that will give you an easy upper hand when defending. The people who complain the most about corvettes are either of completely different skill level or they refuse to equip counter modules or even change ship class. The amount of full healers with not a single counter module against corvettes who just keep dying and complaining is ridiculous.
I agree with Fluffy, the change of available tiers in veteran hurt legendary a lot. Yes, in the past players had to face fully equipped T4s in veteran and they therefore had a mayor disadvantage, however while the loadout differences were significant the skill differences were not. The players playing their T4s in veteran had considerably less experience than legendary players and for the most part were still grinding OBs, modules and ships themself. An experienced veteran player had maybe hundred of more hours than a new veteran player but not thousands of hours. Also you could grind and learn how to use all the modules and OBs in veteran before you went up to legendary where you had to face all the high skill players in squads who played the game more competitively than casual.
Now the situation in very different when you want to move from veteran to legendary. Not only are you faced with a lot of new modules and OBs where you have no idea how to counter them, but you are also faced with players who have played thousands of games more than youself and they also often play in squads with an attitude to win and not with an attitude to grind. Furthermore you have to play quite a lot of games where you are getting stomped until you can finally unlock the OBs und modules you need.
In a sense the problem just switched from veteran to legendary however the magnitude is just completely different. Yes the players in the past had to face T4s with better loadouts in their T3s but these T4s were not fully equipped for the most part, yes these T4 players had more experience but that difference wasn't thousands of hours and they were not so much interested in winning but rather in grinding.
Now in legendary you are facing players in your T4 with T3 modules, a huge experience gap, little to no OBs, and probably you only have one ship in your fleet. The divergence is just too high in legendary at so many levels.