So I've made no secret that I think DOTs are fundamentally boring. However, I don't think that having them in the summoner was some fundamental break with the core design philosophy of the class. People keep comparing how the current Summoner plays to the classic games... like they said, in the classic games, if you could summon Bahamut, you summoned Bahamut. (Or Knights of the Round, or Eden or...) So if we took the classic gameplay loop, the proper way to build a Summoner would be to have this rotation: Bahamut>Bahamut>Bahamut>Bahamut>Ether>Bahamut>Bahamut.

Again, DOTs are boring, but they did need to flesh out the Job some to make it work in a more active system. I think the logic is that with DOTs you could spend more time commanding your pet, so honestly the odd spell out is actually Ruin (Though obviously more time to command your pet means more time for it's AI to mess things up).

TL : DR: DOTs kindof suck, but the reason they suck had nothing to do with job identity.