Were PAR the only thing that mattered, commercial and med indoor growers would be killing it with LEDs, but by and large they still use HPS. Your typical 600 watt HPS has about 220 watts delivered to PAR, whereas an LED has almost all power drawn (save what's used for PC fans for cooling) delivered to PAR. Yet having used both, I'd take a 600 watt bare-bulb HPS over a 300 watt LED any day.
I think the difference is penetration. Typically LEDs aren't quite as efficient at penetrating the canopy, so you have to be on top of the ball with respect to canopy management. Vertically hung bare bulbs seem to be the ticket for results without high maintenance...