From the late 70s to the mid- to late 90s, the X-Men absolutely dominated Marvel - and the comic industry as a whole. In 1995, Marvel’s top 44 bestselling issues - 44 - were X-Men titles. And that wasn’t an outlier. They came to epitomize the edgy, brooding, x-treme, antihero 90s. Starting in ‘92 they starred in a very popular cartoon series that remains beloved - to the extent that Disney has announced that are reviving it.
Spidey was consistently popular but in a much more muted, less impactful way. The Avengers who have starred in the most successful film franchise of all time were basically non-factors. The reason the Avengers launched the MCU is because a bankrupt Marvel couldn’t GIVE AWAY the film rights to Cap, Iron Man and the rest. Hulk was slightly more popular and present in the zeitgeist because of the old TV show, but not by much.
The big figures around Super Hero Island testify to this - the Avengers are confined to a quick-service restaurant, while the X-Men - Wolverine, Rogue, Storm, Professor X, Magneto, Ice Man - stretch the entirety of the land.
All this speaks to a remarkable fact - the MCU hasn’t even gotten to arguably their most popular characters yet, a pantheon that includes just as many recognizable heroes as the universe they’ve already launched. Basically, the MCU has a second MCU in reserve.