Anyone berating OP needs to give their heads a wobble. YANBU, OP.
Yes, it's a global pandemic, but that doesn't give them the green light to shit on half of their staff. And yes, OP technically hasn't 'missed out', but why would anyone be happy that someone else was getting paid more than they were for the exact same hours of work. I mean, us women weren't exactly happy about men getting paid more for the same hours and job role- it's the same premise, isn't it?
Simply put, if you're on a FT contract with reduced hours, you should either take a pay cut to reflect that, or take on more hours than those on a PT basis, with both parties keeping their original pay- pro rata. I highly doubt OP wants to see colleagues (I assume many are friends, too) losing out on money, but just simply wants the set up to be fairer. Which is completely understandable.
I also don't understand why so many people use the argument of 'so many other people have it worse', either. I highly doubt you half of you thought about Billy the homeless man who has a fiver to his name when you were going head to head against Mary for the big promotion. You hardly went and thought to yourself, 'oh, I won't try and get the job where I will earn more money and therefore have a better quality of life, because I should be grateful for what I have and settle at that. Other people have it much worse than me"
Common sense has entirely went out the window these days. Oh, and just as a friendly reminder- half of these businesses will have absolutely no worries in laying off their staff once furlough and whatnot dries up. I wouldn't give so much sympathy and leeway to businesses where, no matter what you like to think, you're simply a number there to do a job.