There are no valid assumptions for port 80 imo. Unless your software is literally a pure http server, you should assume something else has already bound to port 80.
Why do I have vague memories of Skype wanting to use port 80 for something and me having issues with that some 15 years ago?
Edit: I just realized this might be for containerized applications.. I'm still used to running it on bare metal. Still though.. 80 seems sacrilege.