There aren't that many good summoners and we only excel at single target or up to 4 targets, and even the "up to 4" is minimal. At best we have 350 potency going off every 3 seconds excluding burst festers and that's only when all 4 DoTs are up, shadow flare is up, garuda is hitting the target and we're casting Ruin on it which is really for about 10-15 seconds in a normal rotation, and we can lengthen by another 15 if contagion is off CD and then we spend another 10-15 seconds re-applying DoTs and shadow flare. All on one target. 4 DoTs and shadow flare is 170 potency per tick, 145 if the enemy moves out of flare.

A BLM's infinite MP Blizzard is 150 potency, still infinite MP Blizz3 is 220. I'm not sure on the math but the MP sucking Fire is 200+ and I imagine Fire III and Flare are in the 400+ range. Which they can easily throw a couple out, transpose and throw some blizz3's that still deal great damage and jump right back into nuking after a couple of seconds. On more than 4 things