Actually I would like to argue that it is a GREAT mechanic currently as it prevents fleets from being formed with just the heaviest a nation has. It leaves excellent room for smaller ships like Trincs to fill a role in port battles even late game. Similar to how EvE online does it with the significance of light tackle, you need a way to lock down the enemy to bring your big guns to bare.
While I agree that this might seem weird in a port battle, it has been a common theme throughout military history to evade and delay you enemy until the odds are in your favor and that is exactly what I'm seeing here.