One of the biggest issues with corvettes is that their primary guns significantly out range flack turrets, which should be an answer to vettes for a lot of ships. The second issue is that auto repair on corvettes is like having a get out of jail free card. They're hard enough to kill most of the time, even with heavy beam turrets, but when a corvette is flying around with full power to engines, speed amplifier and auto-repair active, it might as well be untouchable.
It also doesnt help that the light cruisers, which are purpose built just to kill corvettes, suck at it. They dont do enough damage to reliably kill vettes before they just fly away, they dont have enough HP to survive getting engage on by a vette and they dont have enough speed to respond to vettes or stay engaged with one. Basically the only thing they are good for is sitting next to healtatos to act as a deterrent and spot enemy corvettes so your team can shoot them down for you since you cant do it alone.