I disagree with many of their decisions, but they’re largely irreplaceable.

There are also a lot of behind the scenes volunteers that do the work, too. But making the front page interesting on a daily basis is no small feat, and from an outside POV that seems almost entirely thanks to those two.

Those stories are promoted by staff because they are interesting and didn't get the limelight they deserved.

The reverse also happens. For example, many cryptocurrency stories are suppressed because they are neither interesting nor novel.

So in short, yes, votes play a role, but without curation, HN would be a cesspit of self promoting cryptoscams and repetitive content. (After all, how hard could it be to fake HN votes?)