About Nightmare : I'm still thinking that he is stronger than on Maxou's or Saitoh's list.
Of course the character is very slow and pretty unsafe. But he really can compensate those weak points.
The movement are something really important in this game. Nightmare's one are top tier.
Combined to his whiff punish capacity, it make him a very good character on my point of view.
Against passive character, his throws are more than correct, and he is one on the best character to break the guard bar.
I think that he is one tier better on both list (C and upper mid).
The only real difference is 3(B) ~ SCH B isn't NC anymore,
That's a legend too. This was never NC. And yes like you said the character was never "really strong" or "broken". Top tier Siegfried was just a legend. But this one became true in people's minds. I guess that Namco just made the decision to kill this legend, and to definitively avoid complaining about this character.
I don't think that Siegfried get a nerf only because of Ring. But because of people like him. People who are able to use strong word like "overpowered", "Broken", "nerf" without any knowledge, just with first impressions. Without any prudence. And now, even if the game is release, this phenomenon is still going on.
"This character is too strong, my character is too weak... OUINNN". This without true justification, just because they saw something who can look likes broken
(I remember when people start to complain about Nightmare's CE).
The game is still young. The general lake of knoweldge about this one is still obvious (an that's normal).
Those people should be really more careful, especially when, like Ring, they have a lot of followers.
Why ? because if not the game will never be balanced.
It seems that Namco is listening to much to the mass community, the mourners. But it's understandable, they are doing more noise than the careful people.
They are complaining over and over again everywhere on forums, they are spamming Daishi's twitter.
With the patchs we won't have a balanced game, but an "avoindingmournerscomplains" game. The game seems really in the hands of the community... but in fact now it's a problem.
I heard some rumors about the next patch. It seems that Ivy will got a very huge buff. Siegfried will be nerf.
If it's really the case : Misssion complete Ring, congratulation. :-)