Kane is a top goalscorer himself and has the seasons to prove it, and then on top of that has world class playmaking skills.
Haaland's ambition, will to score, and finishing are irresistible and indomitable and will very possibly mean he'll indeed end up a "tier above" Kane as a striker and goalscorer, but at this point he's still got most of it to prove, he's starting to be very injury prone, will command crazy wages at a very young age which combined with the person that is his agent will make it hard for most clubs to count on him for a meaningful number of years. Let's just wait and see how it will turn out, shall we?
The age difference of course means Haaland is a more promising investment, but Haaland has a lot to learn and improve (not a good header of the ball, for example), and Kane has been a consistent and well-rounded top performer for a number of years, that's not something to just swipe away. At the moment Haaland is still a much more limited and raw player than Kane.