This is the sort of thing that really makes me dubious about plea deals. We’ve only recently started something of the sort here in the UK.
I can see the sense of getting people to plead guilty earlier rather than spending time and money on the trial.
I can see the sense of prosecutors making a pragmatic decision to drop some charges if they think they can’t or are unlikely to get a conviction on them.
I don’t understand the point of charging this guy with charges of assault while in a position of authority and with sexual assaults and then allowing him to plead guilty to the assault in a position of authority charges and dropping the sexual assault charges.
The only way I can see that being justified is if you think there’s a real strong risk he might walk on all the charges if you proceed to trial.
Otherwise it’s just incompetence, laziness and/or corruption.