On all my RCI cruises the main dining room has been open on lunchtimes on sea days. I am surprised to hear this.
I cruised the Baltic on Navigator and the main restaurant did non open at lunch. Whats wrong with self service? Its basically the same menu. Anyway you should be ashore on some wonderful sightseeing trips!
The main restaurant was actually open the first day, which was a sea day. Certainly on port days it was closed at lunchtime. On P&O the restaurants are open every day.