It's unclear to me why buffets would be more wasteful than other restaurants, particularly in climate change terms.
There's some contradiction in what you've said about minimising waste and demanding fresh foods. If we stick to only the freshest foods, then we waste a lot more.
Surely being able to serve in quantity creates positive economies of scale.
In my observation, buffet customers tend to attempt to eat a lot more by filling their plates with a lot more than they can handle. This is because they’ve already paid for it and believe that eating more is the way to get more value for money. Once they’re in the middle of the meal, they realize that they cannot finish it and that gets wasted. With a la carte, you’d at least have the option of taking the leftovers home.
Some places have a nominal "no leftovers" policy. I'm not sure if and how they enforce it, but the idea is that if there's something significant left on your plate, you should take it with you as you leave paying as if it were something you ordered from the menu.
There's some contradiction in what you've said about minimising waste and demanding fresh foods. If we stick to only the freshest foods, then we waste a lot more.
Surely being able to serve in quantity creates positive economies of scale.