Trim Stab,
The ratings' sackings are an inevitable consequence under Service law of their having failed drug testing. The officers' (consensual) sexual dalliances and poor leadership seem to have been treated as matters for administrative rather than disciplinary action. I'm not sure what they could be charged with anyway; negligent performance of duty perhaps? But very hard to prove that in relation to leadership and maintenance of discipline. A court martial would be required if the punishment was to be discharge from service, and the MoD would then be faced with the prospect of the defendants' lawyer painting the bleakest possible picture of Navy-wide morale in order to get them off the hook.
Administrative discharge, while possible, requires a paperwork trail of continued failing despite counselling; using it on "strike one" would not stand up to a challenge under employment law.