It's all going to rest on the time put into the SMN's summons.

If the summon each have to require about same exp as player to lvl up then it will be difficult to lvl them all.

This also combines with the fact that summons will specialize elementally: ifrit would be good tank against a fire based mob, but the damage wouldn't be great because they would be same element.

What it comes down to is: if you're an epic SMN then you earned it by putting massive hours into lvling yourself and summons plus understanding the complex gameplay mechanics of the class.

Still I refer to the scenario of DDs: NIN tanked in FFXI even though multiple jobs already existed for that role. NIN also was a heavy DD even though multiple jobs did that too. My point is that it was more accepted because NIN was a DD job and everyone generally liked it and it's looks. If you play NIN current day itS even more OP than it's ever been since it literally has so much haste that it crits every second. However, few ppl cry about that; why? Because they look forward to getting that status themselves. Which means that they will have to devote ALOT of time to getting perfect gear plus lvling to cap.

However when a mage gets a shot at the same status; ppl shoot it down hard.

Seems very one-sided.