It depends how much license you give your full backs. If we encourage the full backs to bomb on then you really need two CMs to sit and cover full back areas if possession turns over quickly.I'm not so sure about two holding midfielders, I think one is enough if there's 4 defenders behind. We've had some decent midfield partnerships over the years but they've only had one to do the dirty work of the two.
If we play a flatter back 4 with the full backs playing a bit more disciplined then I agree one holding midfielder is enough.