Realistically these NDAs seem to be more marketing nowadays. Sure, he couldn't talk about it, but Tramell Tillman as William Metzger was well known by those that wanted to know before the film came out.

I do agree it would be frustrating to sign up for a character without knowing the story or long term plan, but that's probably true for most characters.

When Charlize Theron signed up to play Clea she probably thought they were going to fight Kang.

When Josh Brolin appeared as Thanos in Guardians of the Galaxy, how much Thanos story was planned?

Cobie Smulders stuck around as Maria Hill for years only to... Weirdly never appear again in a show that didn't happen.