It is definately harder to solo the nightfall now, not impossible, but definately harder, I believe it was done on purpose as bungie has stated on multiple occasions that they want people to play the game their way, and they want everyone to play everything with a team. I prefer solo play also so I know your pain and empathise with you. They should have increased the difficulty when there are more than one gaurdian running the nightfall and left the solo difficulty alone, it was already hard enough solo especially if youre not using radiance to revive, but since they would rather you go to another site to get 5 strangers to raid with or 2 strangers to nightfall with rather than have a better mechanism in place in game to reach out to people besides the invite method, I doubt the difficulty for the solo player is going to change anytime soon. Just my opinion.