Mate Uniteds team that they started featuring their youth players in had finished 2nd, 1st and 1st the three years prior and was comfortably the best and most consistant team at the time, they would go into games knowing they would win in 3rd gear comfortably, so it was easy to bring in those academy players and get them experience and confidence (which is the key thing), so when the older players moved on they where comfortable playing in a winning side
what your suggesting is more akin to bringing a load of young players into a team that looks a train wreck - more akin to what Villa tried to do and other teams who it went disastrous for. bring in the likes of 2-3 young players consistantly into the team and you could end up absolutely wrecking their development if their initial 5-6 games are heavy losses etc.
The list of young lads you put up mate
Browning is injured still - at least not back playing yet and is 23 by the end of the season
Pennington won't ever be good enough and is already 22
Dowell - not ready right now, and is having by all accounts an inferior season to last year
Galloway - can't get games for West Brom mate - because as a defender he isn't good enough yet, needs to be loaned somweher he will play first
Kenny - i'm a huge fan off, but to start him ahead of coleman would be utter madness
Connely - Not as good a centre back as Holgate, not as good a right back as Kenny is, don't see him really ever breaking into the squad long term - too many players ahead of him
Davies - should be getting games ahead of any of the backup centre mids - looks ready and physically up to the task as well, and is confident as anything
Holgate - looks the part, but was really poor last time he started againjst Norwich unless we change formation - asking him to be part of a centre back pairing will be huge pressure on the lad
In short mate, the young players we have aren't the new Giggs, Beckham, Scholes, Neville
Should some be getting more minutes than they are - maybe so, but to think that they are the magic solution is fooling yourself