i don't think Jack Hughes would be the megastar he is today if he played one more NCAA season and then one AHL season. I think it benefitted him greatly to be challenged for two seasons
It's really not that complicated.
Young draftees by nature come into their first training camp trying to make the NHL with confidence from the previous year(s) excelling at lower levels.
One in a thousand makes the NHL team and starts on the first or second line or in a top-3 D role.
One in a hundred makes the team and starts on the third or fourth line or bottom 3-D role.
Most don't make the team first time, and if eligible for the AHL are sent down to the 5th, 6th, 7th, 8th or 9th lines or 4th, 5th 6th or 7th D pair. They toil in the AHL (or even ECHL) until they reach the 5th line or 4th D pair, and become injury callups and eventually if they keep improving graduate to the main club to start usually on the 4th line (or bottom pair)
They are most often not ahead of those who made the team out of the gate, they are not MORE CONFIDENT, they are simply slower developers or have a lower ceiling. Occasionally, not often, a player who makes the team young crashes out, like say Yakupov or Louis Leblanc. (Just an aside, Galchenyuk is NOT in this category, He remained good enough to play in the NHL for years, improved, and even hit 30 goals and 1 ppg over 46 game stretch - then he got hurt in his D+5, rehabbed badly.....). But more often than not the players selected to play in the NHL after their first training camp do well. Mistakes are more rare than success when professionals are choosing.
Occasionally, players who are close to the NHL level are sent to the AHL with a view to it being a brief stint for them to work on "X". The 'X' is never confidence. Demotions to address a confidence issue would come AFTER a player made the NHL then regressed and got lost mentally.
Last year when Guhle, Harris and Xhekaj all made the Habs out of camp, while Barron did not, this had nothing to do with confidence, and everything to do with defensive positioning. The weakest of the four went down to work on that and came back better after a few months.