Don't get me wrong, anything is possible, but when we can't know all things we can only judge based on the things we do know.
Every team develops a large number of player - a large (but decreasing) number of players are thought to have X potential - very few ever become X. There is only one logical conclusion that can be reached given what we know. Very few players ever actually had superstar potential to begin with.
Still that last part is critical. I mean, compare it to the "opportunities" given to young players under Casey. Hard to believe their handling has maximized their growth opportunities (here talking at least about Ed, Ross and Jonas). Even when Ed played well leading up to the trade, I remember thinking that it still took way too long before Casey caved, started him and gave him a major role.