We shouldn't sign players as back up to our established ones, we should sign players to push them and even replace them.
We aren't talking about a backup to Aurier etc though, we are talking about a backup to Harry Kane. Let's be honest is there a striker in world football that won't cost an enormous bollock who could compete with him realistically?
Competition for most places yes but realistically I don't see something financially practical to go toe to toe with him week in week out.