Even The Last Ship went back on this trope all the time, in that the ship's Captain was leading tactical assault teams on a weekly basis, even in the later seasons when he was an Admiral and the head of the US Navy. Ironically, the one time he actually stayed behind on the ship was the one time they actually needed him in the field.
Except it has nothing to do with military regulations or whether something is a military or not. We see this trope go on on all kinds of TV shows, regardless their setting. Like on cop shows where you see the precinct captain getting involved with every routine crime scene week after week. Hell, just look at NCIS, as the head of the agency, Director Vance should not be the one Gibbs answers to on a regular basis. There should be an Assistant Director or Deputy Director who should be the one who deals with Gibbs and his team for day to day stuff. And that's before you factor in all the times Vance has taken a direct involvement in the weekly cases.
Even in Britain the Sherlock model is rare and was only done because the show was only ever intended to be a small scale semi regular show. If anyone knew its popularity would explode the way it did, they'd likely have done the show in a different format.