I mean, that's what I'm doing, and that causes the class to error like mad for the egi and the sheer raw density of everything is insane, in addition to keeping track of encounter mechanics. The fact that every 30 seconds is a guaranteed 5 oGCDs, you have 5 on one minute, and 3 on the next, the class is just absolute insanity. Then you have devotion (3m) and enkindle (even more for DWT). And, who can forget, TD, which you need to pump out every 30 seconds except once per 2 minutes.
There's something around 19 separate oGCDs you have to get out in the opener, and you average close to one oGCD per every other GCD on a class that's supposed to actually be hardcasting spells. It doesn't play nicely if you have inconsistent ping and the sheer volume of crap you need to take care of, regardless of how it's intended to be used, is way too high for any class to reasonably justify.
I can't think of a single class in the history of the game that has had to pump out as many oGCDs as Summoner has to in ShB, it blows MCH and Bard, the Multitasking champions of SB and HW, out of the water on density. This type of playstyle would be fine on a class intended to handle it, like Bard, Machinist, or Dancer. But it's not fine on caster DPS.