I think Batman was the main character in Batman '89, just in a Burton-esque way. Part of what was appealing to me about the movie (and I imagine what attracted audiences) was that it turned the usual hero/villain dynamic on its head. Not only did we get The Joker's origin story like we would usually get with a hero, sort of a villain's call as opposed to a hero's call, but he's a clown, traditionally a friendly sort of character, and he's standing in the light and smiling and being sociable. Meanwhile, the hero wears all black and lurks in the shadows. He's scary and brooding and gothic. He evokes vampire stories, particularly Dracula.
Horror movies, by and large, are supposed to be about the killer/monster while often not showing much of them. I don't think people would say that Alien isn't ultimately about the alien (xenomorph) or that Jaws isn't ultimately about the shark, but those aren't even that great of a comparison because you hardly get to see them. Bruce/Batman is on screen, and he does get to talk and have a background. A closer analogue would be Bram Stoker's Dracula, and that is Dracula's movie.
I've seen it said that Burton wasn't as interested in Batman as The Joker, but I think you have to look at how Burton demonstrates his interest. First, he has a fondness for "weirdos" in his movies, and he shows that fondness by embracing what's weird about them. Batman in this movie is weird because he's quiet and mysterious and stalks the night like a vampire. Even in the modern comics, he's a hero who behaves like a villain. Having him talk at length about himself or The Joker or Vicki Vale would make him seem more normal, and Burton isn't that interested in normalcy.
Second, Burton was heavily influenced by German Expressionism, and expressionism is like "it was a dark and stormy night" dialed up to eleven, reflecting the emotions/themes of the film in its imagery. The depiction of Gotham City is all Batman, very dark and gothic and mysterious. If we were given a clownlike/circus vision of Gotham City, then I would agree that Burton cared more about The Joker, but we didn't.
I will say that Batman Forever found a way to dig deeper into Batman's psychology while still maintaining mystique around the character, by taking on Hitchcockian elements. However, while I was overall happy with that aspect, one thing that bugged me was that Batman was pleased that Meridian chose to be with Bruce instead of Batman. I've always seen it that Batman is his true self and Bruce Wayne is the mask he wears in public, so it should be the other way around.
