I know what you mean, but it's a bit over simplistic. The question was whether he's worth 91m and the answer isn't always yes. Think what else could be done with 91m - either in terms of building a squad, getting in a few star players, building training facilities etc.
My current Liverpool team has a first choice front three of Coutinho, Origi and Barbosa; would Neymar be better than any of those? unquestionably. Would he be 91m better than any of those (plus wage demands)? I'm not so sure. Look at it another way - I've got Barbosa up front who cost me £9m and has scored 19 goals in 21 league appearances this season. How /much/ better would Neymar be?