I think either your son will stay at school all the time, eat his 21 meals a week and prefer the first plan OR be the kind of student who comes home all the time on weekends and the third option would be the best.
I went to college about an hour away from home. I NEVER went home! College is fun. There is no need to go home. My nephew attends the same school, his home is even closer, and he only came home a few times during the school year, often to do something specific, eat (not that he hadn’t eaten at school, boys just eat whenever they are at home) and go back. Kids just like it at college. Nephew’s biggest complaint was that the dining hall didn’t open early on Sundays, so he had food in his dorm for that.
And they don’t want their younger siblings coming over for dinner. You can always pay for the meals you want to eat with your son at the school, usually about $10 each so no different than Golden Coral (and food quality is about the same!).
Yes, many of those 21 meals will be skipped. That’s figured into the equation too. My daughter had an unlimited plan M-F last year, so she could go to the dining hall at 7, 11, 2, 5 and 7 to eat a full meal, to grab a snack, to grab a drink. On weekends she had to use ‘dining dollars’ to go in the dining hall (or to another place or even to buy groceries), so each of those entries would ‘cost’ her $8, $10, $12 off her flex dollars. She ran out at the end of the year because she’d swiped in other kids who ‘forgot’ their IDs, she’d bought too many smoothies at the gym, etc. This year she has all flex dollars and she’ll have to watch what she spends or she’ll run out of funds again. That’s up to her to manage.