The Templar weapons aren't universal "I-win" buttons, but they can be ludicrously powerful if used right. Have you ever tried putting 4 Longinus lasers and a couple Galatines on a Paragon, plus a bunch of Rhon lasers and Integrated PD AI? It outperforms any vanilla Paragon loadout I've tried by a big margin, just melting through waves and waves of enemies, and the Rhons make superbly efficient PD that makes you essentially immune to missiles.
Another very successful build was an Eagle with 2 x Longinus and 2 x Galatine, it absolutely destroyes anything short of a Paladin, and it can kill that too given some support.
Both need extremely careful flux management however - you can't leave the lasers on autofire, you need to be constantly, actively managing them to avoid overload.
That said, I'd be in favor of making these weapons slightly easier to use (small OP and flux reduction) at the cost of being harder to obtain (stop them from appearing in shops! that just feels like cheating!). It would be fun to have more options in using them, not strictly limited to loadouts completely optimized around them.
@Tommy: also the fighter variant, which I think is significantly weaker and obviously doesn't drop. I say it's weaker because when I was trying to kill Jesuits with a Tempest (call me a masochist) a single normal Clarent would overload me from 0 flux, but I could take two fighter Clarents and end up at around 95%.
@Blaze: if you're playing SS+, check black markets everywhere. The standard small launcher seems to be strangely common on them.