You could well be right, over-eagerness probably got him his red card. When you watch him though...there's nothing there, is there? For example, a young Kyle Walker - he was always super fast. There was something to cling on to, clearly had some fantastic raw attributes. Even players that don't turn out anything special, say a young Tom Huddlestone, he could ping a pass and strike the ball beautifully. There was something that made you think he had potential, even if it didn't work out in the end. I don't see anything with Sessegnon that really buys him some space to develop.
His only saving grace is that we have 1 left wing back, who isn't anything amazing, and we have a dozen or so games until we can buy anybody. And even then, we will probably prioritise other areas. So he may get another chance to play purely by default.