It was the late 70's and I might have been 9 or 10 yrs old. A kid in my class invited me to hang out at house. He and his brother were huge comic book fans and their favorites were The Hulk and The Avengers. I read a few Avengers comics and like them enuff to continue reading. It basically how I got into comics in general. This was right during the end I guess of the Steve Englehart run. He had just brought the Beast to the team and was doing the Serpent Crown story. Just all kinds of crazy stuff was going on. Marvel also was doing reprints of the 60's comics, The titles that reprinted the Avengers were Marvel Triple Action and Marvel Super Action. As a teenager, I was able to get a hold of the original comics.
The Avengers really only seemed like underdogs to me during the Kooky Quartet era and the Roy Thomas /Buscema days say from #50-ish until 90-ish. In those days it was really about these B-Level characters running the show.