That's just the thing though - it doesn't matter if it's just Templar weapons or all weapons. The high OP ceiling of Templar ships doesn't translate to more power if you fit cheaper guns on them. You just get more hullmods or better flux stats. And a much higher TTK against other ships. Offensive power is mostly limited by weaponry, so DR balanced it one way. Making Templar weapons specifically cheaper on Templar ships would be doubling down on that, it's not really necessary. I think the trouble of fitting Templar weapons on regular ships is well represented in the many sacrifices you have to make and the fragile combat performance you get as a result.
The only times that formula runs into problems is when you have Templar weapons with 'too reasonable' flux stats like the Sentenia, Pax Cannon (not technically cheap, but range makes it viable) or formerly the Clarents, coupled with ships that have the stats and spare OP to handle them. A lot of Templar guns aren't great for that purpose already, so it's just an issue of us figuring out the cheese builds so he can fix the remaining ones. Like.. you wouldn't do any better putting a Longinus on a Sunder when you can just fit a HIL with 1/1 flux.
tl;dr: Up Sentenia flux cost a bit and you're golden.
Better flux stats that translate into me being able to slap all those weapons that don't have a too high OP cost but eat flux like nobody else.
Or installing SO and brutally murder anything within 450 range while enjoying even greater flux stats (double venting at all times).
What i'm getting at is making the Templar weapons and ships a "costly but effective" thing when taken separately and a "refer to the ships' chaplain asap" when together.
This would allow DR to make the Templar fleets even more of a powerhouse (pretty much Final Boss or even Bonus Boss staus) without necessarily turning the recovery of a templar ship or a bunch of their weaponry in a "i win" button against anything that is not a massive non-pirate fleet.
Long story short:
Normal ship with Templar weaponry->Ok-ish, better be able to supply the insane flux cost with what little OP it has left
Templar ship with normal weaponry->Ok, is a noticeabily stronger ship with a nice system but nothing too special, there might be better alternatives
Templar ship with Templar weaponry->NOW WE ARE TALKING
Spoiler
My judgement might be affected by enjoying Brawl Minus a little bit too much