I'm comparing a player who wants guaranteed regular football as you said Sessegnon would want, as opposed to players who are confident enough in their ability to stick it out at a big club & prove themselves. You drew the regular football comparison, not me so I can't see why you're now splitting hairs over Sane who came & fought for his place, or Roberts who opted for glory at easily the best team in Scotland.
Talking about Roberts, have you seen yesterday's Sky interview? 12 months after going against the club's wishes & demanding a return to Scotland, he now wants to come back to the PL with either City or another club.
At some point the realisation will hit young players that they can either settle, or push themselves. If Sessegnon does as you expect & opts for regular football above trying to test himself at the highest level, then he's not the player for City.
In terms if Foden & Diaz, they could have done what Sancho & Roberts did, but credit to both players for having the belief in their abilities to stay put, learn & try to prove they deserve to be at City. That's the players I want. If you're happy to settle, then that's your business mate.