The problem is we're guessing and hoping.
He may be Benzema, but we've also had players around that age just aging overnight. Sanchez, Matic, RVP just off the top of my head.
Kane is also one of those players who is also very clearly past his physical prime already, even if he's still in his prime as a footballer due to his technical ability and intelligence. He was never quick but he was a lot faster a few years ago, and his pressing seems to have fallen off a cliff also.
If he was the final piece of the jigsaw in a team that was just falling short of the title, then it would make sense. The problem is I'm not sure we're close to a title next season even with Kane given all the other weaknesses in our team/squad. In which case you have to look at it, is he gonna be the player we need in 2-3 seasons time when we're actually ready to win a title?
If the age profile of our squad elsewhere was young so we could afford to have one player who may be a short-term signing, it may make more sense. But I have similar concerns about the age profile of our midfield and Varane too. We don't want a lot of players hitting a past-their-prime level at the same time.