Can someone give me an in-depth explanation why Summoner is arguably the worst DPS?

[Romsca]

Each class actually gets unique amounts of MP per Piety. SMN gets ~7.25, SCH ~7.5, WHM ~7.9, BLM ~8.25, and PLD ~3.9. These aren't exact numbers; I just tossed on some Piety pieces, found the difference in MP, then divided by the amount of Piety. A SCH with no Piety equipped actually has the same base amount as a BLM, but is a few hundred MP lower...

Turns out blm gets more mana per piety than summoner and the healers. Aikaal, how much mana do you have with your 245 piety? I get the desire to have more which increases your dps. But your resource replenishment is far better than smn. That's the fork in the road, either have large resource reserve or large regeneration.

UUHHHHHHM. Healers don't even get 4k without a party. That would be rediculous, and we literally would NOT run out of MP. AT ALL. like, actually impossible.

I said example. And healers get piety on their gear as an extra stat for 5 total. Blm/Smn only get 4. Sch has aetherflow plus energy drain and Whm has shroud. And in a single target fight that is alright, or we could find the threshold between good sustainability and never running out. Of course, as is our class design, when we start dealing with multiple mobs that are spread out, ie BCoB turn 1 snakes, then we are burning more mana than we can replenish.