Surely they made money from Frenkie De Jong, Donny Van de Beek and Pascal Struik?
True that, I looked at their squad from a date when they had just promoted De Jong and van de Beek but should have counted them as well. Pascal was still in the U19.
But points stands similar (though Ajax indeed got a few exceptional cases of producing five or six top class players in the same generation) that most players will fail even with the best of academies, even if you search for the best youth players in Europe (or now, post-Brexit, in England). But it really doesnt take much to economically regain the money you invested in all those "failed" kids. No need to "milk" someone like Sanders - even if the bid is poor, let him go play some football.