Kane isn't a flair player. That's the first big difference we have on what constitutes flair.
Kane is an incredible player but flair? Nope. Not for me.
I don't know if I even agree with your premise anyway because Kane was always a support striker in the youth ranks, ie. Someone who had good touch, decent vision and passing. What people thought he lacked was physicality and the ability to do what he did at a higher level, not those base abilities in the first place. Those qualities you're probably attributing to flair are qualities he already had before he even broke into the fist team.
To be clear what I mean by training it is, if we buy a player at 17, in terms of flair or creativity what they are is already what they can be. If they don't have those qualities by 20 they aren't going to add them by 25. It's done when you're 6-15.
If you watch youth football you see a lot of the qualities these players have already instilled them by that age. What making it takes is being able to perform at a higher difficulty level and against physically more challenging players. Not the addition of skills or abilities in the first place.