This is a question without a single right answer. Each type of sailing has its own special requirements. Off hand there is absolutely nothing about living aboard that in and of itself makes for good sailing skills.
Bluewater cruising requires a lot more independence and the ability to repair
your own boat, and greater skills in over the horizon navigation, weather prediction, heavy weather sailing strategy, and today seems to imply a range of skills such as radio
communications and leaving and entering countries requirements.
Coastal sailing requires better piloting skills, dealing with currents and entering strange ports. Performance becomes more critical, in particular, light air performance becomes more critical.
Of course if by ''best sailor'' you mean getting the most out of a boat, then the racing sailor knows how to get the best speed, play currents and wind shifts, maneuver in tight quarters, and really get the most out of a boat through sail trim and boat handling.