Using Greenwood as a reason not to buy Sancho is a bit naive to me. Greenwood has bags of potential, he looks like he could be the real deal, but he wouldn't be the first youngster to look a cut above youth level and the reserves to struggle and not make it when it comes to being a first team player. You just never know. He's not guaranteed to be a star. Sancho already is a star. If you can get the best, you buy the best, especially when it's an English youngster like him, those are without a doubt the players Man Utd have always traditionally gone after, and I'm sure that'll be the case under the next manager.
To be fair, I think it's a bit of a moot point as I'd be shocked if Sancho went anywhere in the summer, even though I expect us and other teams to try. So the likes of Greenwood and Chong may get a chance next season to stake a claim.