Capitals are theoretically a late game counter to lighter ship classes.
This is sadly not the case.
Adding an even larger combat focused capital will have one of two potential effects:
1) Caps are even more relegated to the background (pounded by small ships and titans)
2) The titan is useless (too weak to counter the horde)
Unlike most of the other posters, I'm a big fan of the strike craft focused meta. So I don't think that Titans should be immune to strike craft.
But I do agree that caps and titans need a better defense against larger fleets. After all, a percentage reduction isn't all that useful against many small packets of damage, and fleet sizes and FF being what they are, those packets will be overwhelming in short order.
So I'd suggest a flat armor based damage reduction of -X to every incoming packet of damage (ignored by bombers) for all caps and titans, which happens after (not before) damage is throttled by the anti-FF mechanism.
Meanwhile, standard combat frigates should receive limited engagement capabilities vs strike craft, and a slightly higher armor level against them and against caps.
At this point, a pleasing symmetry emerges. Strike craft counter caps, who counter cruisers, who counter frigs, who counter strike craft.
And then there's the titan. Rather than creating a massive damage pooping monster, I'd suggest a vessel with mostly support capabilities, dps and armor slightly higher than the combat cap, and an ultimate that did enormous amounts of damage to starbases (and ONLY starbases).
The way I see it, the game has gone too far in the direction of unbeatable defense. It's not impossible to break a defender, but it is possible for unbreakable positions to emerge. Having a ship that won't really change the fleet battle -- but slaughters the fixed defenses -- is a good means of eliminating that potential for stagnation.
I'm not sure how to handle the corvette. If it's a smaller frigate, it's a useless ship. If it's a larger strike craft, it's probably an alternative to the bomber and fighter that is slower, punchier and in a smaller squadron.
It could also be used for espionage stuff, I suppose, but it just doesn't seem likely to add all that much to the game.