The reason Kane is risky is because there is no chance in hell we are ready to challenge for a PL trophy next year and it's more likely that it will be three years before we have a squad that can challenge on all fronts just as Kane, Casemiro, Varane, Eriksen and possibly even Bruno and Shaw are heading into decline.
This season we have been light years better than last season but we are still light years away from being able to compete for a league title because we are still about three elite players short in the team AND we have no squad depth. We've seen only too clearly how much an injury or suspension to a key player can affect us so can't rely on a strong XI alone.
If you're right that United will still, no matter what do in the transfer market this summer, be light years away from being able to compete for the league title, then of course it makes no sense to go in for Kane...or for Kane to consider United for even a moment.
But I don't agree with your pessimism, although I do concede the possibility that you'll be proven right that we'll be "light years away" from competing for the league trophy in 23/24.
Perhaps you don't really mean "light years" metaphorically, as top four isn't really light years away from the top. But your meaning is clear -- that we have no business going in for players of Kane's age in light of the very real possibility that we'll only be in the conversation for the league trophy when Kane turns 32, by which time his decline will have begun.
I just double-checked and here are some interesting ages, as of today, to bear in mind:
Harry Kane -- 29. Kane turns 30 in July.
Anthony Martial -- 27. Martial turns 31 in December.
Casemiro -- 31. Casemiro just turned 31 in February.
Raphael Varane -- 29. Varane turns 30 in April (two weeks from now).
Bruno Fernandes -- 28. Bruno turns 29 in September.
Christian Eriksen -- 31. Eriksen just turned 31 in February.
Luke Shaw 27. -- Shaw turns 28 in July.
Harry Maguire -- 30. Maguire just turned 30 in March.
David De Gea -- 32. De Gea turns 33 in November.
Harry isn't exactly old by modern elite professional footballer standards. He's no longer a young footballer, without question, but he is at the peak of his career despite playing for a club in turmoil whose squad is woefully underperforming.
Casemiro is still immense at 31 and plays in a much more physically demanding position than Kane. Varane divides opinion on the caf, but in my book he's one of the world's top central defenders. I can go on, but the point is that United are not in a position to wait 2-3 seasons to compete for PL and CL trophies. We may not get there, and we shall see about that, but it would be gross mismanagement on our part to throw our hands up in the air on the ground that we're fukked no matter what we do so let's pass up on the best players we can possibly get so that we can bring in projects who may or may not come good to play with proven world class footballers like Casemiro, Varane and Fernandes.