I think we need to be realistic here. I know that we Spurs fans value Kane at ridiculous prices, but let's face it, Grealish is 2 years younger than Kane. On a 5-year contract they'll get all of his prime years. With Kane they'll maybe get 3 or 4 years. So to think that Kane should be £60m more than Grealish is a bit pie-in-the-sky. If Grealish is £100m, then Kane probably maxes out at £130m. Just look at how much Real paid for Hazard (it was £100m), who was at a similar age as Kane and of a similar ilk as a player. If Kane and Grealish were the same age, then yes, £160m would sound about right.
Now if Levy can get £160m out of City, I will be delighted. But if he gets just £120-130, that's still a very good deal. £100m and Laporte and it is an excellent deal.
EDIT: also need to factor in the wages Kane and Grealish are on. The total cost for Kane, even at the same transfer fee, would be significantly higher.