The problem isn't with Yuna picking a piece that has more nuances. The problem is that she was UNABLE to deliver and hit those nuances, the way Buttle, Chen Lu, Virtue & Moir, and many of those who performed to Adios Nonino DID, and won or were remembered for.
Listen to the commentary till the end about how Virtue & Moir carried the audience with them.
Surely after seeing those performances in the past she must understand that her interpretation wasn't enough?
It is a very difficult piece, extremely beautiful, emotionally varied and very difficult to express, and if not properly performed to by hitting all the nuances in the piece would make the lack in choreography and musicality painfully obvious, and the performance FLAT in contrast to the music with its ebb and flow, diverse pace, different momentum.
Buttle's and Virtue & Moir's versions made it very clear - every nuanced note had to be hit. The performers have to be completely, deeply immersed in the music. It isn't at all a slow piece for coy posing, or for setting up jumps - the music doesn't tolerate pauses and lack of moves, or failure to deliver to the audience by carrying them along on the emotional aspects.
Jeff Buttle didn't even manage to perform at the same level of quality across the competitions, and he took a lot of time to finesse his performance over 2 years. It was also his swan song and he put so much heart into it. From the moment the music started, you could see from his face that he was already in a different place. Adios N is truly artistically demanding, I can understand why Yuna chose it as her vehicle for showcasing her artistry and to grab those PCS.