Well, I think the vast majority of the last 50+ years says differently. Despite that era between 1970 and 1975, X-Men have been the more dominant brand by leaps and bounds. The only other Marvel property that kept pace or just underneath was Spider-Man. Avengers have always had their fans, always, but before 2007 (maybe before Civil War), Iron Man, Thor, and Captain America, as important as they were/are to the Avengers, were kind of B-list superheroes that wouldn't crack the top 10 maybe not even top 20 (all-time superheroes DC [probably holding spots 1 and 2 with Supes and Bats] and other brands included). Supporting cast members like Falcon, Scarlet Witch, and Hawkeye were even lower than that, in terms of wide-spread recognition outside of the greater sphere of comic readers. It wasnt until Marvel decided to force them above the X-Men did they start making leeway IMO. It's crazy how its changed thanks to the success of the MCU.