My experience, based on a recent QE cruise in Britannia compared to the last QV pre-covid cruise:
Much less variety in regards to kinds of fish and meat.
Niecer kinds and cuts were served very seldom, eg only once in 14 days lobster, only once a few tiny scallops.
Basically no real choice in meats, as out of 5 or 6 entrees at least two were vegan/vegetarian, one pasta, one chicken and one fish.
One night the only meat was pork,. Cunard, really?
The diminishing quality was for the most part due to lower qualtiy ingredients, but also maybe due to cheaper ways of preperation, eg. the consommes used to taste excellent like made from scratch, not so this time.
The portion size of the entrees varied a lot and were rather unpredictable. Sometimes they were very small like two tiny little slices of duck.