But is Dr. Strange an Avenger now? In 2016 I would say no, but based on the role he's taken in some of the newer movies, I think it's a bit more debatable whether he is.
What's a good way to judge whether or not Universal thinks Dr. Strange is an Avenger? I dunno, maybe throwing him out on the streets unannounced for (what appears to be) a single night at a hard ticket event. No phone call from Universal complaining about that? Guess they don't think he's an Avenger ¯\_(ツ)_/¯