When you purchase a physical copy of a movie in general; you obtain and retain the right to “copy your copy” and “use it strictly for personal use” ad infinitum.
So yes, it’s completely 💯% ethical piracy to pirate titles you already paid for but found the format to be lacking. You don’t owe filmmakers a second purchase for a new or better format. Don’t bother getting into the weeds over per-screen or per-head copies either; you don’t owe them that either. Just don’t screen a film for more than 3-5 people outside of your immediate household family who are not related to you by blood or name and you’ll probably never run into Copyright Lawsuits… because it’ll never be worth their time to bother.
Pirate away happily matey. Don’t let people fool you into thinking you are more or less ethical in your piracy than what you yourself believes is ethical or unethical. You decide how you will and want to pirate because a pirate is free.