Tbh if we just look at potential, I do think Antony has better raw attributes than Sancho. Left footed of course is more rare, but he is very press resistant, has excellent close control, has a great shot from range, has excellent technique... It's mental/decision making for him. He's ridiculously cautious with the ball while being selfish which is a weird mix on that he'll just ruin counters by not passing it but he also won't go at his fullback too often. Just slows down and plays it square or tries to shoot through traffic. In terms of agility, balance, even pace, work rate, technique/control/shooting ability... I think it's all there for him to be world class. Most of football is mental though, and that's where he has to develop.
Sancho on the other hand is a very smart player, lacks confidence sure but knowing when to pass/dribble/shoot I don't see as an issue for him. I do think he is far more limited with pace/agility/technique than Antony though. Both could go at their fullbacks more often.
I do think there's an outcome where Antony basically turns into Robben. Unlikely, but potential wise it's there. I don't see that level for Sancho, though what he did as a young player for Dortmund was ridiculously good, just more a good not great talent being an extremely smart player.