I dont know Bloxy, there was a period before he was injured when - as far as I was concerned - he was a very, very good player for us. Check out this thread - 28 pages long
https://www.redcafe.net/f6/darren-fletcher-world-class-274802/index28.html and considerable consensus that he is very good - whatever label you attach to that, and however you define World Class. I wouldnt underestimate the job he did for us for a year or so.
Before that, yes, there was a period when he was a little more pedestrian, for me. He was learning his trade. There is some debate about whether people just didnt see his brilliance shining through, as I have seen it argued, or whether he just wasnt that great for a while, with Fergie seeing his potential and keeping the faith. Maybe others saw the potential as well. I dont think it was easy to see on television, in that period, but perhaps the match goers could see something in his positioning and his energy levels or something.
Anyway, the point I am making in a long winded way is that I agree with your sentiment about not seeing what he was doing for us, but only for a certain period, one that is long gone now - well before his injury. If he comes back at 75% of what he was, he will improve our midfield.