Good enough at the time agreed which is why young players should be managed correctly. That doesnt mean they wouldnt be ready, or have the temperament or attitude at a later date.
We've had plenty who we've put in too early down the years who for whatever reason didnt make it. Yes we can never say if they would have done if they had been put in at a later date, but thats down to more informed professionals than any of us.
We've had the likes of Keith O'Halloran and John Johnson thrown in and were pretty much ripped apart in their debuts and then never recovered. I know the reply will be, well they were never ever good enough, but who knows? Luke Williams arguably was thrown in too quick at 16 and never really recovered. Same with Micky Cummins, Mark Hudson, Sean Kilgannon etc. Weve been much better in recent years selecting when the time was right to blood kids (or not) such as Dael Fry, Marcus Tavernier etc.