Of course not, but Rashford hasn't been playing in a team which is essentially built around him as the focal point either. He's been played mostly out wide and it's only now that he's getting a consistent run in the team and he's scoring. In stats he's not too far behind Kane either - Rashford (10G 6A for United) and Kane (19G 5A for Spurs). He's 4 years younger too so he has time to catch up in terms of his finishing skills and OGS is the perfect manager to learn that from too. Nobody is forgetting or discounting Kanes quality and they'd be stupid to do so considering his record since his breakout season and the way he plays, but there are always different methods that will work on different teams and the Rashford/Sancho/Sterling combo would potentially work better in terms of their fluidity. You're right, it won't happen in general because of Kanes quality but when he's injured it won't be too much of a downgrade which is only good for England.