1. I never said "they" conquered anything. Ganen, the first king of Doma did. Him being the first prominent Geomancer who created the Swallow's Compass and learned from the Tengu. The WHM of old didn't conquer anything, they fended off the invasion of the Mhachi (or however you spell it), their casting come from being granted the ability to use the elements around them from the elementals of the Twelveswood (who were not interested in conquering other territories). Did they overuse certain amounts of aether and tip the scales, yes, but they weren't looking to take over anything.
As for my mentioning of anything else npc or otherwise, can you name a single class in the game that performs differently from their role while in dungeons? I can wait but you wont be able to. They could easily have slapped on a heal ability to the Geomancers in Swallow's Compass/HoH if they wanted them to heal.
2. No one is arguing healers getting damaging abilities, if Kyokohu was a healer he would have healed the barrier itself as well as Kinko and you wouldn't have been needed as an Astrologian. You argue that we can't tell what role they can be based off what we have been shown, then you have even less backing for what you want the class to be. Because at the end of this, you want it to be a healer so that is how you are going to perceive it, because you definitely aren't going to base it off what we have.
3. No I 100% know where you are coming from and what your point it. I just don't tend to agree with playing devil's advocate just to argue. And once again, no one here is saying they are the same thing. You really just read "Geomancers and Conjurer are similar" and just go right to typing "You guys say they are the same thing". We are saying they are similar, the game says they are similar and the lorebook says they are similar, so we are saying it would be redundant to have them in the same role. They are using conjurer placeholder abilities because we only have the ONE set of animations for Aero, Stone and Cure. The Sai Taisui have their own for Maledection of Wind, Stone and Water.