And yet, 111111111111111 is still boring. Even if you have cooldowns and resource management. Perhaps healers could have multiple damage buttons that interact with one another, or proc things, or influence the rest of the kit in some way.

You can't make 1111111111 fun just by throwing resource management around it. It's one button, with a second button every 30 seconds. There's no room for growth or complexity there. Fun largely comes from choices. Having one choice means your damage complexity ceiling is...press it or don't press it.