Don't other clubs have similar stats? If I look at us, we've managed to get through Jack and Ramsey. Our record isn't great.
My preference is that he had stayed with us, just trying to offer another perspective.
Chelseas record at bringing through players into the first team may not be great, I think it's probably comparable with other top 4 clubs. Chelsea are also pretty good at supporting players through an effective loan system that helps them make it in professional football. You can see that from the players you've listed above.