Depends what the union negotiates. When they negotiate overtime pay for working on holidays, you typically end up with the lucrative holiday hours being staffed by the most senior employees.

Basically, the junior people get screwed no matter what...

That doesn't make sense. If it's so lucrative that people start fighting to work on that day, even if it's a holiday they'd usually spend with family, then it's probably overpaid. You want to have the right balance so that some will agree to work during those days, but not so much that people start fighting over it.

It's also worth noting that not everyone celebrates these holidays, so for some, that's just a normal day like any other and they wouldn't mind it as much, but appreciate the slight bonus.

An almost universal union truth.

I’ve not heard of any airline doing that for the pilots. I’m not sure about other employee groups. The attitude is that it’s a 24/7 operation and everyone knows this going in. No special days.