Well, he's 20. He's probably not the same category of talent as the two cracks are but who is? He's the biggest talent I've seen in the Bundesliga and considering the development lesser players have taken after leaving Germany, I don't think it's unreasonable to expect him to become a Ballon D'Or contender in the future. IMO he already was the best player in the league last season and that's although the Bundesliga featured players like Lewandowski, Reus or Thiago. I don't think Rashford or Sterling could reproduce his numbers in the Bundesliga, for example. Sancho's dribbling, passing and game reading ability is exceptional, IMO.
But yeah, I can totally understand if you guys don't want to see United paying so much money on single players. As I said earlier, there are many big money flops in the recent past (Coutinho, Dembele, possibly Hazard and Griezmann) and the strategy Liverpool and Bayern e. g. pursued seems more successful currently.