Kane wasn't even first choice for Spurs till Nov last season.(He did score a load of goals in the Europa league in the first few months of course). So you could argue he hasn't even performed over a whole PL season yet.
Exactly. This would be very similar to Liverpool paying £35m for Carroll based on five months of good performances. Kane looks like he has significantly more to his game but I'd rather wait and see how he progresses, especially as the player himself is in no rush to move to a top club.