You pointed out some of the "freedoms" alowed to the smaller class vessels.
Yes indeed , you cannot pirate in a capital ship , but thats not something that people buy those ships for. Since you are a Corsair and the Corsair have 1-3 capital ships (if not more) pinned as their own and they belong to the clan(s) , what do you do with them? Exactly , you RP them , thats what capital ships are for , since they are USELESS for anything else.
Like I said , most players have another charecter of the same faction in a VHF/bomber to pirate in them.
edit : Mule - I agree , I myself never atack VHF's (when they are not atacking me) in my BS , BUT RP wise (I'll need to give a WWII example here)
If a Battleship see's a smaller ship in the water , wich can't even hope to handle one or two shots from the BS , but is allied with the enemy faction to the BS , what would the BS admiral do ? He will sink the ship , 100% sure about that. Because , RP wise , if he let's the ship life , it may warn the main forces about the capital ship's location.