You've brought up a number of topics but I think most can be distilled down to doing the work vs setting the strategy.
As a "social media strategist" my role is completely different being an employee at a brand or a consultant for one. When companies call me today to help with their social I may spend a day doing a training on "best practices" topics without particular focus on their brand or I may spend 12 months working with them as their program grows; it's a function of budget and internal resources.
However for me that role never touches actual posts. Sure I'll craft message ideas, work through posts to suggest better options, and push back on length / broadcast / superlative use but I'm not the product expert, why would I be the one talking as one?
There are however many times when brands do outsource the actual posting and while I'm less and less a fan of this it's about immersion. To move from strategy to doing the consultant / team has to eat, breath & sleep the brand so to speak. This means having trainings, having a clear knowledge of the culture, getting each product, etc to the point where there is a huge amount of trust. It is not something you can start doing for a company overnight.
Participating in a company's social programs is talking to the customer without a filter. There's no review process, no comp stage, no changes. It should not be an side-service, something the provider is new at, or does from time to time. You need to know how it works, know the client very well to do anything more than a general overview.
As for compliance, that complicates it all but just reinforces my first point: the brand needs to lead the charge.