I don't believe we do have the mobility around him, how many times last season were we moaning about the lack of players getting into scoring positions when we're in dangerous positions? All those situation where you hear " we would have scored if we had a striker" that's not going to be rectified if kanes playing playmaker on the centre circle
If Kane comes really deep, lays off a nice pass to kdb in that outside 8 area he likes to be in, he looks up for a potential first time forward pass and sees his striker and primary target behind him, what use is that? Him in that area doesn't give us anything new, he would be playing the false 9 position not as well as other midfield options and with less mobility.
With the exception of sterling (pre dogshit form) they all want to be on the ball far more than they want to be on the end of it. At Spurs, Kane is flanked by son and somebody else like moura or bergwijn, players you'd describe loosely as runners, Grealish wants the ball, as does foden as does KDB as does mahrez and bernardo, gundogan has shown he can do it and reap the rewards but with the likes of Grealish foden and kdb on the pitch I suspect he will be in a deeper role more often than not.
We're not going to spend over £100 million to solve the issue of a lack of presence in the box to then have him doing his best kdb impersonation in midfield. Kanes good at it, it works at Spurs because he is surrounded by players to make it work and spurs don't have anybody decent enough to do it instead of Kane. None of that applies here