“Completely different”? Not really. All coaching requires the ability to teach, communicate, cast vision, problem solve, resolve conflict, set goals, mange time and schedules, delegate, and hold people accountable to their performance
A HC might have a larger scope in terms of their responsibilities, the expectations put on them, the scrutiny they face, and people directly reporting to them— but the skillsets are very similar.
Which is precisely why successful OCs and DCs, and position coaches are promoted to being a HC. And is also precisely why many in the media and the NFL world are scratching their head over the Schotty hire— his coaching resume has been meh