Isn't your gripe with the Qatari government then rather than the airline? They set the rules and guidelines. You called their health authorities rather than the airline. They told you it'd be fine.
I know travel was totally fucked back then, I remember spending many hours trying to figure out what I'd need to enter/leave a country and it always being nerve racking if they'd let me in or not. But at the end of the day, I knew if some place didn't let me in, it'd be ultimately my fault.
I still think the airline did you a massive favor by giving you a new flight for free. That was them trying to not piss off tourists.
Don't get me wrong, fuck Qatar and Qatar airways. I hate everything they stand for. But reading your story makes me think they have really good customer service. I wouldn't expect any airline to do that for me.