It's just common sense that if you replace one player with a better one (i.e. Kane), the team is going to be better for it, even if the tactics are utter garbage and not fit for purpose (I'm not sure where I stand personally on that last point). A hypothetical team of world class players set up with bad tactics will still spank most teams, even if those teams have superior tactics. Jose can muzzle Kane but he can't take away his technical ability.I watched us getting played off the park against Utd, Wolves, Chelsea, scrape past Brighton and get and scrape a draw against Norwich and lose to Southampton all with Kane playing and half of those with BOTH Son & Kane playing together!
Ordinarily, it would be great to see him play, but nothing that had preceded under Jose indicates that his football would be any better if Kane and/or Son are playing.
What are you drawing on that having him back changes our performances?
You mention those dire matches but I raise you 3 vital points won in the CL group stage (Kane's goals literally account for the entire points swing between Spurs and Olympiakos), winners against West Ham, Southampton, Aston Villa and Brighton (only considering open play), and worldies against Burnley, Leicester and Red Star. Those are the kind of contributions you get back again.