Literally the only reason MCH is as weak as it is in comparison to the other roles is because BRD and DNC exist. The developers cannot give MCH the personal damage to actually be worthy of the selfish DPS title without resulting in them becoming the meta ranged job that gets BRDs and DNCs kicked from statics.
The real issue isn't that BRD and DNC's personal damage is low anyway, it's that their total contribution is still low even after their utility and buffs to their party members are taken into account. Again, there's a reason why there are people that literally argue that you only bring a ranged for the 1% role buff more than anything else. That's what a lot of people fail to understand in these discussions. Even now, there's actually more people playing MCH compared to BRD and DNC at raid level nowadays, because at least their total contribution is within shooting distance of the others. The only reason they aren't already the undisputed dominant ranged class right now is because they have one of the steepest learning curves of all DPS in terms of their rotation.
Give MCH more damage without buffing BRD and DNC's total contribution accordingly, and you get what today's Summoner is doing to the other two casters without the party utility.
The argument is saying that it's ironic that casters are allowed to have so much more damage compared to the melee while simultaneously arguing in the same breath that it's okay for ranged to be as behind as they are, when they are also ranged to some respect (not to mention the raise utility that Summoner especially has). It's not like AoEs are being dropped on casters 24/7 like some people are behaving in these discussions.