Honestly, I think mental strength is one area where Vika (uncharacteristically) had an edge on Maria in 2012 - that certainly accounted for the result of their US Open match at any rate.
I do agree that in terms of hardcourts, quicker ones favour Vika in this match-up (even though Vika generally is better on slower ones), and so Vika would probably beat Maria on a quick hardcourt (the very few genuinely quick HCs that are left - Stanford, Cincinnati, Beijing, Tokyo etc.) -- but I'm not sure I'd extend this to grass. Vika's footwork and defence is nowhere near as good on grass as it is on hardcourts, and without stellar footwork she becomes less consistent, and without that she's without her main weapon in this match-up. Plus, Maria's serve would get more cheap points / Vika's return would be neutralised a bit.
Also, just to play devil's advocate
, although clay probably favours Maria, I'm not convinced that it's TOTALLY nid. Imo people are reading too much into Azarenka's weak performance at RG this year, she did actually play reasonably well at her other two claycourt tournaments this year and I think she will have decent results on it in her career. Even though clay will probably always be the one where Maria matches up best against Vika, I wouldn't necessarily expect Stuttgart-style matches in all their clay matches.
For me, the most encouraging thing about their YEC match was that Maria managed to win even though she wasn't outstanding, she just played tactically the right way. I was getting a little bit worried that she/her coach hadn't actually figured out how to play her at all, and that the Stuttgart and first set of the US Open match were just because Maria was on fire and that she wasn't actually consciously aware of what she was doing -- but the fact that in the YEC match, she wasn't striking the ball as well as she can, yet still won comfortably because she actually had a good gameplan, does give me some hope that they have figured her out since Stuttgart (and that their Beijing match was hopefully a blip).