I'm certainly no specialist on the healer specs, but it was my understanding that prior to the revamp, clerics were very powerful in 1v1 and any group with a cleric vs any groups without one (even a group with another healer class) would be a sure winner. Again, I don't know any specifics, such as win ratios in col vs open world pvp, but the sheer defense of a cleric, between armor and invulns, coupled with the near-infinite healing ability (certainly used to be the best of any healer spec) made them incredibly powerful. And when you added Might on top of it all, it seems to have been rather unbalanced.
Now don't get me wrong, I'm not well experienced with the class, so these are all just 3rd person observations and assumptions. I know I lost every time to clerics in col as a ninja, albeit I'm not maxed and ninja's are terrible at pvp until they get lv45+ and it seems to be that clerics in col have an advantage they don't generally have in open-world pvp.
Post-revamp, they definitely seem to be toned down, but I'm not so sure they're much different than Mystic at this point. Used to be that there was little reason to play Mystic when you could play Cleric. I'd say the only reason I would have chosen Mystic over Cleric before was for Port, but even that is just a reason to play a Wizard. I'm not sure where your opinion that Mystic is an offense-oriented class came from though. I've never seen it that way, with only 2 offensive spells, Smite (with a 6s cd) and their awful version of Bolt, which Ninjas have a better version of. Even now, with Smite changed to Ire (or whatever it's called?), they still have the same level of offensive power, and while root might let them get off their two spells and maybe run/kite a little, Clerics were, and probably still are, better at killing than Mystics. Clerics even got another offensive spell that probably isn't necessary/needed, though they did lose Might. I think I'm more or less rambling at this point though.
Summary: I think the overall impression of the server was that Clerics needed to have their leash shorted slightly. I do agree with you, however, that it seems Clerics lost their niche. Keep in mind, though, that I think they were really the only healer spec that had a niche to begin with. Mystics were a joke, and don't even get me started on Disciple (it's a topic for a different thread).
I don't think I'd minds seeing some more group buffs brought to the Cleric lineup, but I'm not sure removing/weakening the skills of other classes (particularly ones who only recently have been made useful) is the way to go about it. Lower the cleric's damage output (removing Might was probably going too far, I like the idea of lessening their normal damage so that with Might added it's equal to their current normal damage), and maybe get rid of that new offense spell that seems a little out of place, and in return maybe make their heals go off a little quicker or grant another party buff that has a self-reduction. Just ideas.
Sidenote: I thought that Mystics had the advantage of being Healing-Over-Time casters while Clerics had the instant heals. Now, it seems every healer has most of the same heals cleric does, in addition to their own specific ones. Clerics do have FullHeal though, which seems like it would be very, very useful, but I can agree a 5s warmup makes it somewhat impractical.