Kane's been there for years and just has a few years left in the tank. Kane shouldn't leave for free, his contract protects that, but demanding £160 mil. isn't fair game.
If United didn't pay a dime for Bruno and if were here for years and says he wants to try something new, personally, i wouldn't stand in the way. Demanding £160 mil. and then wondering when the players is unhappy is standing in the way, IMO.
Grealish has about two more years as a top level footballer than Kane -age wise. To me that would be worth more money. Letting Kane leave for a 'reasonable' price (£75-£100 mil.) could be a sign of goodwill for years of world class performances and giving up more money he'd easily could have gotten elsewhere.
Spurs and City aren't rivals, Spurs haven't won the league for ages, they just happen to play in the same division. How it has come to that was unfair and comparable to winning the lottery, but that's for another story.