I agree with you. At first, I couldn't understand the program and was baffled at her cold looking performance. She could have chosen more enthusiastic music, but I think she chose this music because she didn't expect to get a gold medal in Sochi. And she said, she always wanted to perform this music after crying on Jeff's adios nonino that David Wilson showed her(she said it was the first time that she cried watching figure skating performance).
As someone said earlier, The music is about elegy to late father. Therefore, Yuna's performance is different from ordinary sassy Tango. It's about a memory of past, most of the performance is subdued, emotions are burning inside, occasionally a flash of lightness and smile, even a little flirtatious, and reflecting the memory of good times. in the end, reminisce of everything: good, bad, ugly.
After watching it many times, I dare say that this program is a masterpiece. Never gets boring even after watching many times.
Again, thank you for your thoughtful analysis and appreciation of the performance. It does get better the more I watch it. It didn't quite have that same "pow!" effect in Sochi, which may be part of the reason why the judges didn't go for it presentation wise? It wasn't immediate, and reading the synopsis of the piece it was indeed composed by Piazzolla as an elegy. But like a fine wine, it ages well, and gets better the more you look back at the memory of it.