It's actually better to find your level sooner. If you actually don't have what it takes to be at a top club, its better to know early and find your level. There are no scenarios where sitting around as a backup is better. Its better for the club, sure. But almost never the player.Times move in year ago a lad at 20 would think playing cup games maybe 1/3 starts in league and of the bench 10/15 games be fine!
Whose to stay he leaves and struggle end up on the bench there!? He is now at the best teams in Europe bide your time improve then At 22/24 either he is a first team player as in starting 40/ 50 games or he leaves a much much better player! Not all will be a palmer..
The thing about waiting around as a backup is that other players your age are gaining playing time and matching their mettle against the types of players keeping you on the bench.
In 2 years, a kid with similar talent to Nico playing 40 games at Dortmund or Espanyol will quickly surpass Nico in the eyes of the world.
And once said player is being chased by the top clubs in 2 years, City too will join the fray. Thats just the cycle. To any young player who isnt part of the core 14-15 players, my advice is yhe same. Leave. Make your mark. If you are as good as you think, we'll come get you in a year or 2.