This is just non-sense....having more of any unit is better, corvettes are no different...
Throw a couple of any frigates at a powerful target, and the frigates will get massacred....swarm your target with a ton of any frigate, and the target will easily be overwhelmed...
Advent units in general have more DPS per fleet supply than TEC or Vasari units, and that is why Advent fleets are dangerous...it has nothing to do with the fact that they are "more numerous"...Corvettes are no different, they have a high DPS per fleet supply and per cost...
Additionally, due to the geometric nature of combat, slight performance differences between units are more accentuated when the numbers are larger (in Sins, shield mitigation and passive regen are part of the cause for this)...this is true for all units, and it is why the ridiculous power of CVs is most apparent when they are in larger numbers...
If a unit that costs less fleet supply is continually outperforming a unit that costs more fleet supply, it is not because the of the fleet supply difference...it is because of the combination of DPS, damage tables, resiliency (HP, shields, armor), regen rates, and attack patterns (fighter style or non-fighter style)..,
The entire premise that units with less fleet supply are inherently more powerful is just completely fallacious...in fact, if you gave all units the same DPS and HP per fleet supply, larger units would be superior....