Well, Sancho has played eleven matches for bvb this season, about half of them as a starter.
Foden has appeared for City nine times (probably started a bit less) but was also injured for the part of the season when he might have been expected to play more.
Brahim has appeared eight times.
Sancho has played a little bit more, but it's not a massive difference. It's not as if his move to BVB has catapulted him into the first XI. They're all in the same boat, at big clubs, learning and being eased in.