I think you're talking about two different things though. It's not mutually exclusive by any means. Sure, I'll give you the point that people aren't going to see a superhero movie because of the romance, but I do believe it can add something to the movie that makes the audience invested. It adds a human element that can be difficult to convey when dealing in stories that most people can't inherently relate to.
No matter what, romance shouldn't be forced on heroes/antiheroes that rely less on it, where it is less a core.
While Batman is a romance character, some of his movies feel like they force it down your throat too much when the films could have done a little less with that aspect given the stage of his life, etc. I'm looking at Chris Nolan and Rachel Dawes.
The Punisher is another character where you perhaps see movies/shows trying to force romance or flirtation in where it doesn't belong.
Things I love: Batman, Superman, AEW, old films, Lovecraft
Grant Morrison: “Adults...struggle desperately with fiction, demanding constantly that it conform to the rules of everyday life. Adults foolishly demand to know how Superman can possibly fly, or how Batman can possibly run a multibillion-dollar business empire during the day and fight crime at night, when the answer is obvious even to the smallest child: because it's not real.”
Though in the Batman comic books, Bruce proposed marriage to Selina and she said yes. That's pretty much the current theme of the current run of the Batman comic book, Bruce and Selina are a romantic couple.
Going on adventures together. And now they are going on double dates with Clark and Lois. At least in "Batman Returns" when Bruce asked Selina to live with him, she flatly rejected the idea.
Romance in stories can be great. Problem is, their execution in superhero adaptations is pretty terrible a lot of the time for many reasons.
If it wasn't for the romance subplot, a lot of action movies wouldn't even have a named female character.
It's all the writing. Iris and Barry is an incredible distraction and poorly done. Lois and Clark is classic and organic to the story. Cap and Carter - nice touch. Optimus and a Dodge Ram truck - well, let's not go there.
RE: Flash television show
this is a whole other conversation, but a lot of the heat Iris gets isn't because of her relationship with Barry