I don't know if Froome is the strongest or not, but I agree that people saying he is based on thin evidence. I think if the two were on different teams we might have a very close Tour. Froome could gain some time in the mountains, but we don't have near enough evidence to say it would be several minutes as some assume. Wiggins would likely gain time in the time trials.
Anyway, Froome's best interests lie in doing his job. How many teams want a guy who would blatantly defy team orders anyway? Also he'd be far from guaranteed of winning with the big closing time trial coming up.
If he continues to perform like he has in this Tour, he will have other GT opportunities.