I agree with you but 3 is just an arbitrary number in this case Spider-Man, Wolverine, Captain America, Hulk, Thor and Iron Man(with X-men and FF) are the most important properties to Marvel with Black Panther, Deadpool and Captain Marvel probably moving into that group with continued strong performance.These are fun topics that happen in a lot in sports who is Goat or who is in Mount Rushmore but random number is always design to keep someone deserving out and cause discussion. Not even DC Trinity is really a Trinity of equals Batman and Superman are clear more popular with Wonder Woman realistic being a group with Flash and Green Lantern surprisingly Harley Quinn isn't that far off.