The avatars would have probably benefitted from having specialized roles rather than being capable of attacking with some support.
No they wouldn't. The job is pretty much perfect as is, except for the penalties applied. It should be a moderate DD and moderate support, but it is a slightly below moderate DD and useless support. Less global timers, slightly less MP costs, more ward potency and viola, perfection.

Well, you'd have to tweak avatars favors too if you want to count it as useful, and same with spirits. But Summoners have all tools they'd ever need... if they worked.