We can't expect every ship to hit above its class. Idris hits above its class with its single railgun and anti cap missiles. . . .
The Idris actually hits below its weight class. If you compare it to the Void Bomber it is much less heavily gunned, but like the US Iowa class battleships from just after WWII, it makes up for this with very advanced damage control and such. The Idris is a defensive ship, meant primarily as a picket or tank type ship that keeps fire off the larger, more capable classes like the Javelin, whereas the Void Bomber is all offensive guns bristling everywhere. VB's are attack ships the size of an Idris.
I figure the Polaris will hit below its weight and be a anti fighter ship.
That's a good bet.
I could see these hanging back with a carrier and protecting it while its fighter and bombers are deployed.
Typically Corvette class are not seen as particularly useful in fleet engagements. They do exactly as you say, but their real use is normally alone patrolling and running down smaller craft such as anti-smuggling operations, or anti-piracy, where their enhanced speed can be of real use. That speed is useless when the ship is moving with larger, slower ships. The best example of a modern Corvette are the new US Independence and Freedom classes of Littoral Combat Ships. If you look at their missions you'll see they shine in anti-piracy, but in fleet engagements are generally for things like mine laying and other relatively non-combative roles. Putting a Corvette on a picket is almost sure to have it destroyed as has happened in many battles of desperation over the centuries.
And of course, the Corvette is the typical first choice of pirates who want to chase down and board larger capital class ships.
