I think she makes an excellent assist for beginner and intermediate players, or players who don't use combos and just mash buttons (like myself). I think she's especially great as an assist for AI/CPU opponents in Original Quests. I have her set up with my ""Ultimate Ultimecia" Original Quest (That isn't the quest's actual name since you don't have enough characters to type it with, but that's pretty much the point of the quest).

Of course, I play the game with cheats so my gameplay experience may be totally different than others who don't.

For starters, my Ulti (actually, it's Edea) has +1000% assist charge, so Yuna comes in a lot and almost never misses. She rarely gets blocked or locked, too, and allows Edea the time to follow up with powerful HPA's. It makes Edea feel like a real "Boss Fight" in Dissidia to me.

I'm going to be posting a video (and download) to my Original Quest to show how OP My AI/CPU Edea is, though I'm sure more advanced players will find her more annoying rather than challenging when they watch it. I personally love my Edea build, though. She's a tough fight for me and the Original Quest I'm working on has pretty much nothing to do with FF or Dissidia so it's a bit of breath of fresh air.

In the meantime, check out my OP Firion build on YouTube

Watch it on YouTube for the build in the video description.