That may be right, and he could very well be a player to build around. But the reason I said it's unrealistic is because we already have a fairly expensively assembled squad with lots of new players and some established, and that makes things difficult.
If we are going to build a side around him, that would involve building a side with a target man for him to play off, a dynamic midfield with pace to run off him and create space, full backs to overlap, defenders who pose an aerial threat from his set pieces. Judging by his performances so far, it seems like it would be a complete rethink, and an acceptance from Koeman that he was wrong. That rather than being the magical final piece of a puzzle, he's actually the 1st in a new one.
Because personally, I don't see a team with him, Schneiderlin, Gueye, Klaassen, Sandro, Vlasic and Rooney ever working, certainly not on the evidence of his performances so far. He is not giving us an extra dimension, he is giving us a taller, slower version of the dimensions that are already there.