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

[ShinryuReishiki]

Personally, I'd like to see Enkindle with a 4 minute cooldown so it lines up with Rouse + Spur. As it is, it may as well be on a 6 minute cooldown. I only use it with just Rouse if it can hit multiple targets, or if waiting that minute would stop me from getting a third Enkindle.

So, I had a bunch of math done, and then Ifrit screwed it all up with his Enkindle. For some reason, Inferno does damage disproportionate to the listed potency, at least compared to his Burning Strike attack.

The difference is that Inferno is a Magic (Fire) attack while Burning Strike is a Blunt attack. Ifrit's physical attacks do less damage per potency than magical attacks. This is why even though Ifrit is doing 180 potency every 3s with Burning Strike + Auto Attack, the damage is only ~20% higher than Garuda's 100 potency Wind Blades.

Some attribute the damage per potency differing due to physical and magical defense of targets. Personally, I suspect that Ifrit's physical attacks use the Physical Damage stat of the weapon, such as Dreadwyrm Grimoire having 82 MD and 58 PD (Although it's not shown in game), but I haven't done any significant testing to support such a claim.

[Viridiana]

Some attribute the damage per potency differing due to physical and magical defense of targets. Personally, I suspect that Ifrit's physical attacks use the Physical Damage stat of the weapon, such as Dreadwyrm Grimoire having 82 MD and 58 PD (Although it's not shown in game), but I haven't done any significant testing to support such a claim.

The latter explanation seems much more likely, unless someone wants to explain why ladybugs outside Ul'dah should have the same defense stats as Bahamut.