Considering that literally nothing has materialized for Iron Man outside big blockbuster movies led by Downey it is highly likely that his popularity will wane quickly once Downey is out.
You could say the same for the entire Avengers franchise. Downey is the linchpin of that group of actors.
I agree that Downey Jr. is the biggest reason Iron Man went from the B-List to the A-List, the other reason being movie scripts that efficiently managed to exploit that charm and charisma of his. Without him, the character is still second/third-tier, especially when it comes to comic book sales.
The individual talents of the actors playing the other characters does help propel the popularity of the entire franchise to heights it wouldn't reach if it were actually just Iron Man & Friends.
Downey plays a very big role behind the scenes as well.
http://deadline.com/2013/05/robert-d...-fight-491675/
I think one very big reason why Batman is such a popular character is thanks to Batman: The Animated series coming out in the early 90s, and the series carrying over to later series within the same universe such as Batman Beyond and Justice League.
If other DC characters like Flash, Green Lantern, Hawkman, Shazam, Martian Manhunter, Black Canary, Power Girl, and Wonder Woman had their own animated series in the 90s or 2000s with the kind of writing and art style that made Batman: The Animated Series such a hit, I think people would find those other DC characters to be just as popular as Batman too.
Top 10 Favorite Comics as of September 2019
Image: Unnatural, Isola, Monstress
Marvel: Magnificent Ms. Marvel
IDW: Samurai Jack: Lost Worlds
Other: Chuck Mullin's Bird Brain, Huda F's "Yes, I'm Hot in This," Nathan W. Pyle's Strange Planet, Dirk Manning & K. Lynn Smith's Hope, Samurai Grandpa
^^ Most of those characters you listed like Manhunter, Hawkman, Canary, Power Girl have really weak villains and supporting casts. They will not last past 10 episodes if they had their own show.
Look at all the characters who had their own books for decades upon decades. Superman, Spider-Man, Hulk, Iron Man, Batman all either have a great rogue gallery, or a great supporting cast, or BOTH (in Superman, Spiderman, Batman's case).
I'm not familiar with Manhunter, Hawkman, Canary, and Power Girl's comic history, but I do agree that the rogue gallery and supporting cast of Superman, Batman, and Spider-Man have been very essential to their success and popularity.
However in the case of Power Girl, I think an animated series with the writing and art style of Jimmy Palmiotti and Amanda Conner might be popular and give the character some new-founded popularity.
Top 10 Favorite Comics as of September 2019
Image: Unnatural, Isola, Monstress
Marvel: Magnificent Ms. Marvel
IDW: Samurai Jack: Lost Worlds
Other: Chuck Mullin's Bird Brain, Huda F's "Yes, I'm Hot in This," Nathan W. Pyle's Strange Planet, Dirk Manning & K. Lynn Smith's Hope, Samurai Grandpa
I feel like the setting of Batman, his costume, the fact that he doesn't really have any powers, lives in a cave... is pretty much what attracted me to his Verse.
He's very different from the typical superhero. But yeah I feel like the Villains play a major role. Penguin, Harley, Joker and Catwoman are just great villians and unlike most other Villains, these Villains can stand on their own, whether in comics,movies or whatever.
"Bat-Mania" started on 1966. Joker, Penguin, Riddler, and Catwoman joined public pop culture consciousness since; most of each appearing in further incarnations of Batman / Super Friends / Super Powers cartoons, then action figures; Joker, Penguin, and Catwoman, also with slew of action figures, co-made hit movies, before that CARTOON-I mean, "animated series".
Patsy Walker on TV! Patsy Walker in new comics! Patsy Walker in your brain! And Jessica Jones is the new Nancy! (Oh, and read the Comics Cube.)
In Batman comics I always like villain characters. They are more sensible and attractive look.
Kudos to Maureen O'Connell of Scholastic for getting us the Harry Potter series.