To me Loch was never OP before because two charged shots did more damage than one Loch shot.
It was a very situational ammo type with limited uses, but when done right, could be spectacular. The gunner would often have to bring mallet, which meant he couldn't rebuild anything. With the changes in the rebuild times, that would have probably been all the balancing you'd have needed for Loch.
Right now it just seems it's been nerfed out of use. I'm the sort of person that likes everything in the game to be useful and in use; so perhaps it may never be what it was in 1.13 but I'd love it to be something that people would have a reason to want to use over other ammos.