They have abilities planned which the scripts are not yet done for. For now, they're just regular battlecruisers that aren't especially good yet.
Ah for 15 point expensive until I would recommend that they do ISDII+Torpedo Sphere damage perhaps and give them strong shielding. Less damage than a Praetor perhaps, tough as guts something like that.
Torpedo Sphere+ISD II clock in at 12 points, for the extra 3+ cost of unit make it tougher.
They struggle to kill frigates.