It seems to me there's a lot of hand wringing here over nothing. Under Rule 6-3b, the Committee had the authority to have the last 2 groups play in together. Also, the players no NOT have the option, on their own, to stop play due to darkness. Only the Committee can declare it too dark. Once that happens, the player can complete the hole he is playing (Rule 6-8b). To my knowledge, the Committee did not declare it to be too dark.
As for who was advantage by the way it was done, clearly Phil and Rickey were advantaged. Standing in the fairway on the easiest hole on the course, trailing by 2, they both knew they needed eagle to have any chance. By seeing Rory's tee shot before playing their second shots, they had valuable information they otherwise would not have had. If Rory had hit it in the water, eagle may not have been a necessity. Once Rory's ball is in play, eagle is the only option - exactly what they would have believed if Rory had never hit. Under Normal circumstances, Rory would know exactly what he needed to do before playing his second shot, as an eagle either would or would not have been made. By playing his second shot before Phil and Rickey finished, he was deprived of valuable information.