The problem does not seem to be too few categories of Diamond levels. The problem is the success of the program itself. The Crown and Anchor program and the innovative ships built by RCCL Intl, has led to a tremendous customer allegiance for both Royal Caribbean and Celebrity. This has led to an explosion in Diamond and above on Royal, and Elite on Celebrity.
The solution, at least for the larger ships, appears to be that the company as a whole and the Hotel Director in particular must be willing to devote one of their large lounges as the Diamond Lounge each evening between 5 and 8:30. I just got off a 13 night transatlantic on the Liberty of the Seas. They used the Sphinx lounge as the Diamond Lounge and it worked out very well. If there was a problem it was that there were far too many people who arrived at 5 and did not leave until 8 or 8:30. I guess free booze is an alcoholic's fantasy, but surely all those folks were not alcoholics. Late diners should show some restraint and not overcrowd the lounges early. If they wait for the early diners to leave for dinner we would all be better off.
Also, I don't think that the majority of Diamond Plus and Pinnacle members use the Concierge Lounge in the evenings, they seem to prefer the Diamond Lounge where they can associate with fellow frequent cruisers.