Herrera is NOT an ACM and he is better as b2b, then ACM, he just can cover more positions.
I am mostly happy with what we brought as Blind, Shaw and Herrera were players we needed. Rojo needs to find form, so we have to see, but at least he is cover for 2 positions, which I think is very good, as we didn't have ANY left backs. We probably over paid for him, but....
Now, di Maria was a luxury signing, but one we can afford and one which could make the difference, just he didn't perform as a winger this season, so LVG doesn't know how to use him properly, even if I do think that he can work as a winger if he would work more with FB's and stops being selfish (of course for him to work as a winger, we would need to play deeper, but because we try to press more he only played well in a diamond and it could be a problem). I agree that for that money we could have maybe bought a defender and another CM, but I can't say that I don't understand it at all why he was bought.
For Falcao I do think we didn't need him, especially as he wasn't fit.
So, I would say that most of the signings we have bought were good choices, while I do agree that the di Maria money could have been spent better, but I can live with that transfer.