Would be interested in seeing a list of players Chelsea have let go when they were young who are now playing well at a side in a top league. I can think of:
Ake - sold at 22, now at City
Guehi - sold at 21, doing well at Palace and in the England set up
Tomori - sold at 23, doing well in Serie A
Livramento - hot prospect sold at 18
Lamptey - sold at 19. Like Livramento, probably impacted by Reece James, but still, they're playing RLC at RWB currently..
Abraham - sold at 23, doing well in Serie (and did better than his expensive replacement)
Salah - sold at 24 after 2 years out on loan, became one of the best players in the world
De Bruyne - sold at 23, became one of the best players in the world
Lukaku (first time) - sold at 21, became high profile goalscorer and bought back for a huge fee.
Boga - sold at 21, has done well in Serie A, less high profile than some others on this list but still a decent player.
They're just such a weird club. Letting players like this go, and then spending big on players who haven't necessarily done any better. I know it's a numbers game for them and for every one they sell who goes on to do really well they probably sell two who drop down divisions, but it still has to hurt seeing their former youth players do well elsewhere. They have some decent young players on the fringes at the moment too, like CHO, Ampadu, Pulisic, Chalabah, and I wouldn't be surprised if one or two of them leave and go on to have really good careers elsewhere.