I know what it is, but I don't know why it should be. The point of the nightmare campaign is that you can't just slap together a random team and just about always win either, but that apparently doesn't stop there being a normal campaign for people who can't do the nightmare version. It doesn't stop there being dungeons for low levels, or an arena (though the less said about the arena the better), or even faction crypts. Nor does it make it a good idea to increase the campaign difficulty across the board because some people feel that the nightmare campaign is too easy for them. Does the fact that even newer players can take part in those activities take anything away from the rest of it? I would say no, and I don't see the harm in allowing just about anyone access to entry level of the content, especially when completing it is also a requirement for the advanced quests that you get access to well before mid game. The forge materials seem way out of place if the intention is to produce gear that you can't (or at least souldn't) use by the time you can forge it. If this is content new players shouldn't be thinking about, then the game sure has a strange way of communicating that information. Either way it's a failure on the part of the developer.
That is in regards to the difficulty in general. When it comes to bosses, no, I don't like there being arbitrary restrictions that give preconditions that you must meet. Restrictions that limit your effectiveness, sure. I don't mind the dragon being immune to TM reductions, because it doesn't stop me from using champions that do TM reductions, it just means that the particular part of their kit that does it doesn't contribute. Forcing certain aspects is another thing. For one because it locks people out for not having that particular precondition (which is certainly worse for newer players), but also because to me it makes things less interesting the more limits you have and the less variation is possible. Perhaps you're cool with that, in which case, good for you. Doesn't mean I'm obligated to agree.