The problem is that “every” Marine needs to be a combat killing machine first and then his/her MOS second. Every Marine is expected to be able to take up command of a squad, platoon etc. on a minutes notice. That requires being trained and tested in leadership in the combat arms and the ability to pick up the weapon and perform in combat.
Having worked with Marines over the years I was always impressed with the maturity of the Marines I dealt with. The junior Marines were just as impressive because they were trained to take the lead when the situation presented and to follow orders to the letter.
Take away boot camp and you lose the leadership part for the Marine “recruit” who has skipped the advancement route. The other Marines will not willingly take orders from those that did not earn the insignia, and if these new “Marines” are not sent into the field or deployed the others will resent them.
VERY well said!