The Diamond Plus level has been around for several years - this isn't a new category or attempt to block out lower-tier members. However, yes, they do receive a higher level of onboard amenities due to their status (along with other perks).

Royal Caribbean has never been a "luxury" line - they're firmly in the mainstream Contemporary category. All lines have made some cuts, and I've never ranked RCCL as tops in food - far from it. What they offer is a lot of activity, broad demographics, and easy vacations. Other cruise lines definitely focus more on service and food, smaller ships, and specialty itineraries.

Perhaps it wouldn't have cost much to keep you happy, but I know of many Diamond members who were abusing the Concierge lounge nightly, with more than a couple mixed drinks and food. They bragged about how it knocked their onboard tab down to almost nothing. RCCL wouldn't have eliminated the perk if it cost them "nothing or next to nothing" to keep. Believe me.