I'd say it's unprofessional to out & out leave the interview. Maybe for practical purposes it doesn't make a difference (though it can be a small world sometimes and you never know when something might come back to haunt you) but there's a certain amount of social norm & politeness involved, even if your own sentiment is "well they aren't respecting my time so why should I care?"

Also it can come down to just a bad recruiting/HR process and the place itself is perfectly fine to work for, and maybe that doesn't come through in the initial screening nonsense but you figure it out from the final round. Or you just end up not having a choice if the market is tight and you would end up wanting to take the job for the paycheck even if it's only 6-12 months while you find something better.