They're not "supposedly" promising, they are objectively promising. That doesn't mean they are all guaranteed to reach their current, projected ceilings, but they're being given a lot of unexpected games due to our injury situation, which is accelerating their progress (or, in some cases, may allow us to more quickly identify deficiencies and either move on or work through them).
At the moment, I don't know if our season will end with a whimper, or if we'll be having another red hot go in September, but I'm certainly having fun watching events unfold and waiting to find out. In either case, and more relevant to this thread, I am absolutely certain that what we're going through right now, and the games these promising players are getting, is going to result in a team that is stronger next year than it is right now.
Again - speculation. No one can say with any certainty based on undeniable evidence, that Carlton, Richmond or Geelong's youth is going to be stronger than another teams. We can guess based on history, given that younger players tend to improve with age, but we can't say whose is going to improve more other than to beat our chests and with utter bias state that our team will be the best. I'm sure Geelong's youth are 'objectively promising' for some supporters and even 'experts' but in the end, its all speculation.
Richmond and Geelong have a great track record of developing youth but only the future will prove who is better.