Most family holiday dinners that I've seen are neither fully hosted nor are they true potlucks. Instead they are exactly what they sound like: family dinners. At family dinners in many families, it's the norm for everyone to participate in the meal, but the nominal host to do the bulk of the work and provide the space, as well as organize the participation.
I can't imagine a family holiday dinner where my parents or grandparents or aunt made every single thing, and "hosted" in the true and proper fashion for dinner parties. It's not a dinner party, it's family. My mother is going to ask my brother to bring the green bean casserole since he didn't leap to volunteer something, and that's not rude. He can say he'd rather bring something else, or he can bring the horrid casserole, but he can't bring a bag of frozen green beans and whatever else goes in that horrific concoction and hand it to my mother right before meal time.
It's family. Help or get out of the way, but don't agree to bring something and fall down on the job.
You write this like its some sort of universal law. Its not.
In my family whomever hosts, hosts fully and completely. It would be downright rude to bring a dish to one of my family's dinners unless it was pre-cleared well in advance, and even then I doubt it would be agreed to happily. How rude and dismissive of the hosts! Its not a picnic, its dinner, and there are certain rules of formality to dinner, consistent rules that are amped up when there are more family members present not toned down. Men would be expected to wear ties, and women make-up - there are no jeans at my family dinners! Formal table manners are observed. Children do not get special foods. Etc. Casual is reserved for when you are alone.
Now obviously not all families are like mine, I have through friends and beau's and my husband and my other extended family experienced totally different types of family dinners, not to mention what I've seen on TV... and I have to say what you describe is something I've only ever seen on TV or in movies. I know of no actual family that operates in that "everyone pitches in with the food" way. There is nothing wrong with how your family does it (it sounds fun!), but I hardly doubt its a case of how "most" families operate.
This was a SIL - she married into the family. She honestly, even after a few years, might still be getting used to things being done differently then her family of origin.