Kane plays outside of the box very often. Haaland’s first instinct is to get inside the box. Kane comes short. That doesn’t mean Kane doesn’t score goals - it means he scores a lot of the goals that we don’t struggle to score currently.
He has good numbers, of course. A lot of them are also from penalties, Haaland either doesn’t take them, or when he does, rarely scores them. He is more of a 6-12 yard striker than Kane is. Kane wants to drop deep all the time. Which isn’t even so bad when he plays in a team that doesn’t play with a recognised #10. We do.
Rashford, Martial and Greenwood are not goalscorers first and foremost, and their first instinct isn’t to score goals. If that were the case, we wouldn’t have to force them, beg them and get them all sorts of striking coaches to convince them to get into the box. Their first instinct is to drop deep or drift wide. Kane’s is now to drop deep. Haaland’s is to head directly for the 6 yard box.