All of these examples of it not working isn't a cause for concern? Doesn't it seem like signing a big money striker as a "backup" with him and everyone else knowing that he's a backup has some inherent problems? You say Chelsea only have one half decent striker, but it's not for a lacking of spending money on strikers! Doesn't it seem that even in situations where two strikers are competing for being first choice when one of them pushes on to a Kane level of excellence the other almost always struggles and is eventually shipped out as a "failure".
Do we want to take part in a Emirates Marketing Project like merry-go-round of expensive backup strikers coming and going because that's the big club mentality?
To me it makes at least as much sense to say Kane is our first choice striker and will remain so, no need to try to sign someone as good as him. If he gets injured it will be a big blow, it's not the kind of blow we can completely prevent. Let's instead sign someone who will be happy in their role as Kane's backup, someone with potential, someone who can develop. Someone who ideally if Kane at some points decides to play for Real Madrid or Barcelona might just ideally have stepped up meanwhile to the point of being able to take over.
It's a cheaper solution (allowing us to spend our money elsewhere) and it's not an inherently worse solution in my opinion.