A backup striker would be nice but it's not the end of the world.
This fella is being relied upon and that's all there is to it. ETH isn't viewing him as a young, inexperienced striker he needs to baby. Look at his words. You don't say he is the one we've been waiting for just to put him on easy street. He didn't take the pressure off with that statement, he made clear how he views him, if the fee wasn't already obvious enough. Apart from when he's talking about transfers ETH is very direct and straight forward, so take it for what it is.
For the backup role we still have a combination of Martial and shifting Rashford into the role and playing Garnacho who is extremely talented and needs game time. Sancho is a real desperation choice, I don't like that. But I guess at a push.