In WWII, the term "Destroyer" was invented to describe a new class of boat that was created specifically to destroy small torpedo boats and subs. These were originally called "Tin Cans" for they were much smaller, lighter and more agile than their cruiser cousins. These little Destroyers can be considered cap ships, but only because of their in-fleet function.
By this older definition, the HH is a Destroyer. It runs interference on fighters, bombers and anything else that wants to sneak up on a fleet and attack from close range. By contrast, the Perseus is actually in the patrol boat interdiction class, meant to intimidate with its big guns, any non-martial vessel into compliance. If the Perseus guys are doing it right, they never have to fire their guns at all.
The Polaris is another class than either of these, and for best results really should be considered a hunter of opponent cap class vessels, more like a submarine than anything else. Hence the name--harkens back to the first nuclear subs of the late 1950's, and the ballistic missiles they were able to launch (both "Polaris".). Earliest reveal on the Polaris was that it was created to combat Vanduul Void Bombers and that is its ideal purpose. Like the original Corvette, and the Perseus, you can bring them into fleet engagements, but they are not intended for this, and unless they're turning the tide of battle, you are throwing them away using them against big cap ships. Putting several Perseus against a Vanduul Marauder is basically throwing them away. Using a Polaris against any sort of cap class vessel is fine, given the elements of surprise and evasion one usually does not have in fleet engagements.
