I don't think most people who are critical of Valencia really give a hoot whether he's the symbolic captain or not, or whether he can speak English. What I care about is how poor he is on the ball and how detrimental he has been to high tempo attacking football. It isn't a new thing - he's always been quite poor on the ball and terrible at crossing - but it's really been in the last 4-5 seasons that his deficiencies have turned us into such a lop-sided team going forward.
At Wigan, and at United pre-injury, his weaknesses were compensated for by his pace, power and aggression. And his shitty deliveries were compensated by the fact his aggression got him into so many crossing opportunities he could afford to mess up most of them and still finish the match with an assist. But about half a season after his comeback from injury his confidence in running at defenders seemed to take a big knock, and as a result his crossing opportunities really diminished. And with that he seemed to lose all confidence in his shin-smashers as well. This marked the birth of "turnaround Toni".
This was obviously partly why SAF moved him to right-back. He probably also thought that if Valencia wasnt going to make the most of his pace and power on the ball, he might at least make use of it off the ball. But it still meant we had a right back who would receive the ball in advanced areas, dither with it, slow everything down, only to turn tail and play it back into midfield, repeat ad infinitum. He's done okay defensively at full back, again due to his physicality, but in the modern game that is far from enough.