2000 hours isn't all that seasoned, and he had less than 50 hours in that type. He was accomplished all right, but not what one would call seasoned.

In fact, the root of the word "seasoned" means "prepared" and he clearly was not prepared for the events leading to this incident. That through no fault of his own, hence he was not formally disciplined.

The Marines expect someone of his position to perform above and beyond their training. He didn't, so he lost that position with no formal discipline.