I betrayed to templar about a year ago, so pre-repent, pre-mythical etc. Templars are overpowered as all hell.
Best group HP buffer in game, a templar is a prime choice to solo heal dps groups on tougher fights, because simply stated templars have a huge buffer vs all other priest types. What other priest class can get all mages in dps gear to approx 10k hitpoints?
Arcane ward, not only is it great for people wearing chokers, but most AEs that matter tend to be arcane or have an arcane component to them.
UB, no other priest class offers a stoneskin other than the warden clicky, but that's not enough, we also get SA as an additional way of preventing damage on our target. So yes shaman wards heal before our reactives, but the reality is, without casting a single thing during an encounter, we've already prevented a ton of damage.
Repent, not as limited as our reactives with + heals and can easily parse for an 8k heal. Looking at heal parses and from what I've read on these forums when a single target spell counts for 20%+ of a heal parse in comparison to the other level 80 spells handed out to priests, that's a tad overpowered
Sanctuary, 40s at master and specced cures. Imo for how powerful the effect is, the recast should be lengthened on it. 40s of being able to do whatever you want. Considering the procs on mobs out there that fear, stun, stifle, etc. This is a huge advantage to any group with a templar in it. Much more advantageous than the inquisitor/defiler breaks.
Crowd control, Inquisitors at one point had the edge in this. There was a time when as an inquisitor was king when solo healing. Sadly, invocation got nerfed and then nerfed some more. Similarly the inquisitor root used to be a lot more effective and had a shorter recast. In comparison to other healer archetypes, our daze and stun put us leaps and bounds ahead of others. Fear has its uses, but most times when needing some kind of crowd control, its because you've pulled more than your group can handle, or are forced in a situation where you have no choice but to do so. More often than not, fear will only create temporary relief while bringing more bad news to the group. On the other hand, we get the ability to prevent a mob from auto-attacking for a decent amount of time or even outright stunning them. Sure sometimes these spells get resisted, bad luck, improper debuffing, etc. But nonetheless these spells make the templar a more powerful heroic content healer than the other classes. Just make sure these spells are at the very least adept 3. Masters tend to be really cheap as templars don't tend to see their usefulness.
Hell Divine Arbitration is one of my favorite spells to heal someone up with when I am halfway across the zone dealing with tells. I mean they even gave the templar an easy-mode for you are busy in tells.
The templar's biggest issue is power management. So long as the templar has power, the group should live. So far as power management if that's your issue at 80, power roots(can have one from each tier and with RoK everyone got a carnivorous plant they can claim, recipes can be found on eq2i), at 80 get 1-2 groups to farm trash in TR (Jewelery set)and Kill Pantrilla(Honor of Pantrilla); both of these can be done with less than a full group, but if you're not confident in the gear/abilities of your groupmates aim for more than one group, signets from the status merchant. So even before getting any power gear, just the roots and signets should get you out of most sticky power situations.
Bottom line, post-mythical, no other healing class fits as easily into a group as a templar when it comes to raiding. Prior to that, a templar was still recommended on every raid, due to the stoneskin/sanctuary/buffs they brought to the table. Now with Repent, mythical, steadfast are you surprised some guilds out there want to raid with as many templars as they can get their hands on for the tougher encounters?
The only complaint I have about Templar is that its not half as fun to play as an Inquisitor, but its highly more efficient to raid with.