I'd agree he's technically and in terms of IQ a much better player than Antony. The problem is he doesn't show it. Sancho hasn't helped himself at all at Utd, he seems lazy on the pitch, makes poor decisions and it feels like he only comes to life when he feels like it. Aside from a few moments here and there he hasn't looked anything like the player we saw at Dortmund.
ETH see them every day and if you're much more talented than the next guy but he's still being picked ahead of you every week and so if someone else. Then you are most definitely doing something wrong.
I'm one of those people who sees that type of wide player and thinks, he needs a specific type of fullback on his side to get the best out of him. Dalot and AWB are not the players to do that, I also think Antony needs a different profile of fullback. People laugh at that suggestion but there has to be a relationship there, they have to dovetail and compliment each other. If a player likes to come a bit inside like Sancho, then you need a marauding fullback that goes down outside to get the best out of them, create space and movement for them to operate in those areas. If you have a fullback like Hakimi, even TAA, I genuinely think you'd see a different side to these players.
Even if you go back through teams, Rafael/Valencia and Nani, Salgado and Figo at Madrid, Alba and Neymar at Barca. There was a dynamic there that got the best out of both players.
Edit: even if you look at Arsenal where they had the likes of Eboue and Lauren at fullback,not necessarily great players but they worked because they provided a balance and complimented the likes of Ljungberg and Reyes out wide. Then you had Cole and Pires etc on the left.
If anything I think that's where the club has failed to get the best out of Sancho on the pitch.