First of all we ain't "developing" Iwobi the lad is what, 24?I think that inability to develop players is a major problem with the club that we really should be giving a toss about.
Secondly, two young lads wanting out because we didn't give them automatic starting places and expected them to earn it in training like the other senior pros is not "an inability to develop players".
The argument against what you're saying is simple. DCL, Richarlison, Holgate, Godfrey.
Those are 4 young players in development who Everton Football club have improved. It also helps that those 4 lads aren't little crybaby primadonnas who want out of the club after a year.