In *theory* destroyers are the best option here. Use Small weapons (or possibly Medium weapons that have good tracking), and computers and possibly modules that have good tracking as well. Look at the tracking of your weapons, and of the tracking you get from your bonuses (including computer, sensors, etc.) and try to get them close to (but don't bother going over) 90. That's where Corvettes top out, and any tracking score beyond that is wasted. Don't bother pushing your own evasion too hard; it's hard to get destroyer evasion higher than the tracking on a corvette's weapons, and anything less is wasted effort.
Unfortunately, the whole "destroyers are the counter to corvettes" thing seems to exist more in the devs' minds than in reality. In practice, your best bets are either "more corvettes" (you say "with same fleet power", but if you're on the defense you should be able to have more fleet power than they do because the distance from your starbases should be shorter) or a mixed fleet with some high durability / high evasion ships (or a station) as a distraction and a bunch of long-range weapons (on ships, or starbase + platforms) with their tracking boosted as high as possible (which won't be anywhere near 90% but it's OK to miss half the shots if your base DPS is 3x as high). A titan (or two) with the tracking-bonus aura can help a lot here, although a perdition beam tends to be somewhat wasted against corvettes.
High range weapons are surprisingly effective against corvettes, because corvette swarms lose DPS as a pretty linear function of the damage they take. Dealing 50K damage to a battleship fleet may have literally no effect on its DPS, if the damage is spread across a few ships (as it tends to be). Dealing even 10K damage to a corvette swarm is going to take a significant number of them out of commission (dead or retreated), and each one gone is either three guns or a gun and a missile launcher that are no longer shooting at you. Since corvette weapons are short-ranged, those ships killed or sent home in the first volley or two will never get to fire. For this purpose, artillery computers can be more beneficial than tracking-optimized computers, though consider using artillery precog computers (which boost tracking a lot, though they aren't the best at range or rate of fire) if you have them.
Point-defense (PD) guns are usually a good idea, unless you know the enemy fleet is eschewing missiles or is using swarm missiles (which are so hard to shoot down it's a waste of time to try). PD guns are actually also good against ships (except if the ships have a lot of armor), but if they don't have armor you're better off with autocannons (similar base DPS, range, tracking, and penalty against armor, but with bonuses to anti-shield and anti-hull that PD doesn't have). If the enemy is using PD guns, consider mounting Swarm missiles yourself; most of them will get through once the range is too close for the PD to kill them in time (and they have decent tracking) and they'll soak up a lot of PD shots (often to no avail) that would otherwise be chewing up your ships. Swarm missiles will cost you a lot of DPS so they are a bad pick if the enemy isn't also wasting a lot of DPS on trying to kill them with PD, but if they are, then you can make the enemy waste more DPS than you are giving up yourself (and missiles bypass shields, making them more effective than their raw DPS numbers suggest).
Tactically, you want to watch for where you and the corvettes will meet, and position yourself as follows:
- If tackling with your own fleet of corvettes or destroyers, have them basically on top of the enemy, or at least travelling in tandem if they are multiple fleets, so that they engage together (this is always a good idea for short-range fleets, since you want them to spend as little time as possible with the enemy out of their own range). Such fleets should have admirals that boost movement speed and/or evasion (if it isn't already at 90), otherwise almost anything positive except range is worthwhile.
- If you have long-ranged heavy-hitters, you want them to enter the fight as soon as possible after the tacklers engage, but ideally from as close to their own maximum range as possible. They'll fly towards the fight (even artillery computers insist on trying to get to range 80, even though your max range is probably more like 140 for an artillery battleship) regardless, so don't be afraid to be at a range where initially only your spinal weapons can hit. Such fleets should have admirals that boost range and/or tracking if possible, and health and/or rate of fire otherwise.
- If you're on the defense, try to have the starbase in range. Even if it is nothing more than an outpost plinking away with a single missile launcher, it will distract some portion of the enemy fleet, who will spend a relative eternity wearing through its defenses. If you're on the offense, try to get the enemy to meet you well outside of starbase range, and ideally on an initial trajectory that will keep the fight from drifting into range.
- Don't be afraid to set your fleets on "Passive" if trying to ensure the enemy meets you where you want them to; right-clicking the enemy (if even needed, even "passive" ships will automatically open fire on an enemy within range) is a lot less pre-battle micro than constantly countermanding your ships' desires to go chase the enemy out to the edge of the system where your starbase and/or artillery are out of range.
Finally, remember that corvettes die easily, and war score is largely determined by kills. Be ready to retreat (especially your larger ships) if it looks like the battle is going against you. You may technically "lose the battle" but actually lose fewer alloys worth of hulls and less war score, and thus end up winning the war by attrition. Do ensure your ships' retreat point (home starbase) is set somewhere as close as possible so they spend the minimum time MIA and also the minimum time flying back to the front for the next fight.
Good luck!
