Yes, it absolutely gets turned into fish food. You might have strong feelings about it being dumped in the ocean, but it does get turned into fish food.
And yes, the crew mess im sure it gets extremely repetitive. But also that Indian food everybody raves about being able to special order for the dining room? same food that the crew mess is getting.
I travel with allergies and my serving team wanted me to order an advance for the other meals. I know everybody that travels with allergies needs to order at least their castaway lunch in advance.
If your main dining team is being dismissive of your allergies, you need to be speaking to a head server immediately.
Also, I think if you’re very concerned about the amount of waste that’s happening and you’re very environmentally friendly cruising is probably not for you. There is very little environmentally friendly about cruising.