Yes, it's disappointing, but it's not the worst I've felt after a Marion loss. The round of 16 loss to Bammer at the US open a few years ago when Marion was sick and had 2-1 40-0 in the 3rd set is probably the worst for me. Bammer didn't even play well that day, Pironkova did play well today for example, Marion had 4 game points in one of her service games and Pironkova SAVED all of them. Marion should have served better, but that's tennis for you. I really wanted her to get to the 4th round at least and she did.
Tbh, I don't think Marion has played well all year and therefore doesn't have the confidence to play high risk tennis anymore, which is what she needed to do to win this match. And movement will always be an issue, hence the 40+ winners by Pironkova. It's likely that Marion will spend the next few years around the top 20/15, having the odd great tournament here and there (last the year, the Australian open, Stanford and Bejing), but she'll never be able to perform consistently well because she simply isn't good enough to do so