Corvette have innate evasion % built in. Which makes ship with terrible tracking weapons have more trouble with corvettes. Corvette has 60%, destroyer has 25%, cruiser has 10%, battleship has 5%. Some weapons can negate the evasion advantage and some can't.
An entire fleet of corvette can move MUCH faster than destroyer etc... In-system travel-wise not FTL. For battleship you need afterburner and other tech to make them match speed with a non-upgraded corvette.
Corvette has a dedicated hull to mount torpedo which does lot of damage especially if the enemy doesn't have any PD whatsoever. Sure you can use a cruiser to mount a torpedo but it has less evasion and more weapons can hit cruiser evasion-wise.
You can also build swarm of corvette that can take overkill hits from missile, missile and PD mechanically-wise are iffy right now in 1.4 and 1.5 may change that, saving your super-expensive battleship from dying.
Right now there isn't an easy way to collect your enemy's ship design and figure a way to counter-build. IE if your enemy uses lot of missile that is easy to tell and you build more PDs. Not as easy to tell if your enemy is using anti-armor weapon or anti-shield. Should you shift to have more armor or shield?
So keep that in mind.