@gsmt47471015 has answered most of your questions, to add to his comments, I would say that pre covid there were usually more interesting speakers on our 35 night cruises, and there were some changes during the cruise, as well as some that were on the entire cruise. The guest artists do usually do the same number of shows as shorter cruises, and are changed at similar frequencies, except of course on the longer sea day legs.
The MDR menus do repeat but pre covid the daily selection was higher, so I hope the executive chefs will now be a little more creative on longer cruises.
We do enjoy the longer cruises more than the shorter ones, however the return atlantic crossing can seem more tedious, especially as the weather deteriorates.