Exorcist is a lot worse than a lot of people say.
First of all, yes, the total damage numbers are high, but the initial damage is pretty abysmal per hit, so you need to be stationary a lot to achieve a kill (i.e. you need to stand close to the enemy to deal damage with Koinonia, Aqua Benedicta, and possibly even Rubric as the enemy can escape your beam = no more damage).
Then, while you have an elemental advantage for a lot of monsters, it’s not so easy to kill the stronger ones.
Ground Destruction skills will clear your Aqua Benedictas, moving enemies (e.g. Zaura) will move out of your Rubric within the blink of an eye and Koinonia can’t even be used solo, so it’s only useful in team battles, and only deals damage when the team is positioned correctly.
In the majority of cases, my Koinonia does nothing because people either cluster together or run around crazily (maybe they don’t even know what the skill does?), spreading and closing the “holy net” randomly on monsters.
And, as its base damage% are so low, it deals ± nothing against the majority of strong bosses (except the additional element & blessing damage which ignore the defence).
As for the rest of the skills, Gregorate is pretty useless except for clearing debuffs (it doesn’t even work that well with zombies to explode) and mobbing monsters, same with Entity, so I don’t use them except for pulling aggro in 99% of the time.
Engkrateia is completely useless after the nerf as it only provides 3-6 seconds of protection if not close to a camp.
All in all, given the many downside the skills have, the damage is justified.
It’s also pretty much the only viable damage aside from Druid and Bokor in the Cleric tree on the magic side.
About Zealot vs Exorcist:
You forgot that Zealot has an easy way to increase damage via critical hits.
Given Zealot has free crits and crit rate with Beady Eyed, Zealot can also make use of the high critical attack boost of Krivis, which can tremendously boost the overall performance of the Class.
Zealot can also benefit from elemental boosts (e.g. by advancing to Taoist at Rank 11 to double the damage of Fanatic Illusion and give another 50% attack boost to every single attack skill in its repertoire via Storm Calling) and use Deprotected Zone(if we assume the monster stays in one place for Rubric & Aqua Benedicta, we can also assume that for Deprotected Zone) and Zalciai for easier damage & crits.
To be honest, I think Zealot is in the clear advantage since it works well on its own, has useful buffs and can be further boosted by e.g. Taoist.
Exorcist is strong in theory, but in general it suffers a lot from bad team-play and the monster A.I.
I think it’s clear that Exorcist is by far not as good as the majority of people think.
It’s two damage sources are dependent on the enemies positioning, it offers little to no support (1 debuff clearing every ~30 seconds) and is really costly to invest into to have any results at all (Rubric needs 2 expensive attributes to work well[still ignores a lot of mobs even after some mobs died due to the initial mob limit], Entity needs at least partial investment to even hit any mobs at all, Aqua Benedicta also requires another attribute to have sufficient hits to kill stronger mobs).
Its 3rd Circle is also underwhelming, a Circle of Dievdirbys for Laima or Zealot for Fanaticism or Druid for Lycanthropy is more efficient at boosting the overall damage & performance than Circle 3 of Exorcist,
which tells you a lot about the damage improvement per Circle.
