Summer tiki(y) -+Def- res worth giving DC

Well, I never advise giving an unmerged seasonal unit such an expensive skill unless you absolutely love that unit.

With that said, if you plan on getting more merges, or you just absolutely adore her, then I say go for it, although it mostly depends on what build you're wanting to make for her.

In my opinion Summer Y!Tiki can't use DC very well unless you have a boon in res, while her res isn't bad it isn't good either, after the first engage she will hardly have enougth hp to tank a second mage. And in your case is even worse since yours have a bane in res

I'm with Yezzo here. Her magical bulk isn't amazing to begin with, and the superbane really doesn't help. I would expect her to fall in one hit to a Naga tome and maybe even a strong red mage. Green Olwen also has a decent chance at taking her down because blade tome bonus damage ignores the weapon triangle. (By comparison, my summoner supported Nowi wins against Naga tome if she's near max HP. It's kind of disgusting.)