I find the issue with using sub battleship classes in most cases is dps projection. Yeah you can fit a proteus to have the damage of a megathron but you pretty much need to be at point blank range. Your best options when going sub battleship are:
Beam fit Legion, single Web and two TC.
HAML fit Loki, dual Web and two GC, armour tank and immobility driver sub. I genuinely think this is superior to the tengu because of access to drones and greater versatility with the guidance computers and webs together.
HML tengu, mwd fit to keep range. Use minimal tank and cram in target painters.
Shield fit myrmidon, use small blasters or autocannons to eliminate any frigates that get close.
The loki is probably the best option, but there is a reason people use battleships. You can get away with training it to 4. You don’t even need to train a battleship weapons class as you can just use rapid heavy missile launchers on a drone boat like armageddon or rattlesnake. The arbitrator or prophecy is a great option for level 1-3 though.