An airline can't re-write the FAA's regulations. The FA's authority comes from the FAA, not the airline. It is the airline that makes the FA a hospitality worker, the FAA sees them only as crewmember's who duties involve the saftey of the passengers.

I suppose an airline could staff the flight with the minimum requirement FAs and then put additional non-FA hospitality workers on board. That would avoid the dual-role issue but it wouldn't be very efficient labor wise.

I think a better solution would be for management to do a better job at earning and keeping the respect and loyalty of their employees so that they stay motivated and enthusiastic about their jobs.