Considering they've both lost a considerable, but comparable amount of weight, I don't think we can assume that his commitment is truly any less than hers, only that SHE thinks so, and is very vocal in expressing it.
I do think she seems to have "written her father off," and maybe that's better for both of them. I don't think that she was being a good support to him, and she definitely wasn't getting what she needed from him either. They may just have very different styles and methods of weight loss. Maybe he's more committed to diet, and she's more committed to exercise. Maybe she just sees his weaknesses and not her own. Who knows?
I do not think that the show is like most (reality tv or otherwise) in that issues of truth, fairness, and balance take a back seat to telling an entertaining story. I think the editors themselves also have biases that will affect their editing, and thus the picture we see. If any one of us were editing the show, we might create a VERY different episode (and it might not be any more "accurate" because of our own biases).