Generally, cards that attempt to have multi-element costs will be tricky to code (see my Duality series for an example of what was done to get around this.)
Gameplay-wise, I am planning for the Sages to be mono-element. There are other cards that are mono elements and have spammable abilities (Vanadium Warden and Arctic Squid), so I don't think this will be a problem.
Also in comparison to Explosion and Steal, this is less effective, but has the benefit of being on a stick. It's also relatively cheap to play and use.
As for thematically, think of the Delay effect as being the result of the Air Sage channeling the winds to delay permanents (sort of like a windstorm - it slightly damages things but normally doesn't obliterate them like a volcano would). However, like a tornado, it's unpredictable, which gives the Air Sage little control over what Permanents are delayed.