Not unknowns, but hardly popular or known as spidey, hulk or even wolverine. Not even close.
Again, this 'not old enough' doesn't work with me. I've posted a lot of examples about their exposure in the media in, at least 30 years, and it pales in comparison to the exposure the more known characters got.
And more, the Avengers only became 'popular', in comics, (and marvel biggest brand) in the mid 2000's, with Bendis basically detroying them and adding Spider-Man and Wolverine ( I wonder why!) to the mix. After that, specially with the beginning of marvel studios, they started putting top names to write the classic avengers' main characters (IM,Thor, Cap). Before that, in the 90's and early 2000's, all the 'hot' talent went to the x-titles, spidey, etc.
Hell, even he awesome Busiek&Perez run on Avengers, while appreciated by fans, was hardly a top seller.