I'm not saying they aren't allow or try to score, my concern is can they deliver the quality of crossing and passing when their main asset is their shooting?
For example Rashford, if we ask him to do more crossing and passing to striker, his number of goals can be significantly impacted (lowered) while his number of assists might not increased significantly due to his crossing and passing quality aren't as good as the likes of Mahrez or Giggs (for instance). The reason is because we ask him to do something that is not his main asset. It's like asking Kane to play on the wing to dribble past players but doesn't mean it will work because Kane's quality or main asset isn't his dribbling and pace.
Ultimately what players do in a match is not so rigid as you potrayed. When Ronaldo played on the right wing, Fergie gave him a freedom to go middle and get the end of crosses and still wreck havoc with his dribbling when his position allowed him to and it was quite effective. Later when Rooney was moved to the side and Ronaldo played centrally, Rooney still scored plenty of goals. And our front three interchanged a lot, we conquered Europe with that frontline. And yes, it's true, had Rooney played more centrally and focused on shooting only, then his number should have been higher. But I believe for managers the most important thing is the team then the individual records, not vice versa. And I believe Rashford isn't as bad when it comes into passing, not that I see Ten Hag asking him to put 100 crosses ala David Moyes anyway. If we bring in a top CF that is to take pressure off Rashford and so they can form a much better team than focusing on one person only which makes us harder to defend against. The last thing we need is relying on Rashford to the point where he gets injured or burnt out again. Because you can say goodbye to any target we have if that happens and we still have the same CFs next season.
Can Kane play on the wing? not effectively. Can he sometimes occupies where Rashford normally is (by the way he can be a wide forward than a pure winger) to draw fullback in so Rashford can go to the center? yes, he absolutely can and he's not bad at link up plays either. If your focus is to make sure Rashford get to be as productive as he can be in the terms of goals, you can do that. But that is a detriment to the team when you can also bring in a top CF. I wouldn't be as pessimistic as thinking our forwards can't pass/cross properly when we have nobody up front to get on the end of those and score goals. Football is also a positional game, sometimes it doesn't take a Paul Scholes to create chances if the team structure is solid enough up front. Right now we have essentially a statue that chases people around and when we don't, the replacement always loses form due to injury/not 100% to play. We have seen it firsthand how Bruno & Garnacho refused to pass to Weghorst when they could have. That's not good and it has to change. How can we score lots of goals, which has been our problem this season when we're missing 1 person up front?
But yeah I guess if we add Kane into the team, Rashford will naturally do more through passes and crosses without the manager asking him specifically for it. Since that means he will see more opportunities to do so.
tldr; it's not as rigid as you think it is. And in modern football, the more options you have the better for the manager.