From what I've noticed playing Summoner now, is that is it simply too punishing once you make a mistake.
If you accidentally click Bane or Fester without DoTs, you are set back on your entire combo from Dreadwyrm to Bahamut by 60 seconds waiting for Aetherflow to come off CD.
An easily QoL change is to make it so that you gain Aetherflow is given regardless of whether you have DoTs on them or not.
Having no damage done/Misusing the ability to its full potential should be the punishment.

Devotion is also very uncontrollable.
It is counterproductive to move your Ifrit/Garuda to a certain party member, using the ability, and expected to go through your rotation smoothly.
It simply cannot be done effectively. You lose out on your potential for damage, and feels overly complicated for simply no reason.
There are Role abilities that are programmed to be used much better than this. This should be changed to be more usable.