The difference between Son and Kane right now is that Son still looks like he can move and find space etc. to get a shot off. Son's shot and finishing has been atrocious though, that I admit.He's out of form when it comes to converting goals. No doubt. So is Son for a long while now (he had a streak at the start of the season, since then nothing) which is a problem. Neither are looking clinical at all. But bad runs for forwards happen, we don't just hit the panic button.
But when your forwards are out of form, giving them 1-2 chances a game isn't helping.
Physically, Kane just looks so off it. The were a few moments when he was in the box in sort of a dangerous area and he couldn't get a shot off. The old Kane or any decent striker would have put in a move, then got a shot off. But when he tried to make any kind of moves, he just looked like he was gliding in slow motion, with no real threat.