RCCL doesn't charge you $200/person/day to visit the buffet, nor do you tip on a $200/person per day concept.
You tip, what $6/day, to waitstaff in the mandatory tips (with the other $10-$12 to stateroom and then general staff)? So, per meal, if you eat breakfast, lunch, and dinner, you're leaving an equivalent $2/tip per person on the table for all the service you received at your meals.
That's about the tip you'd leave at a land-based Golden Corral for a meal, not a served sit down meal, so they've pretty much put tips at the lowest tipping rate restaurant type for US restaurants.