Concierge crowding can be itinerary dependent. It is an issue, and frankly, I wouldn't be surprised if RCL removes concierge lounge access for Diamond Plus members in the near term. Soon, all of the ships will have Diamond Lounges, and when those refits are complete, I don't think it will be long before Diamond Plus are there if they aren't booked in a suite. Oasis will introduce this concept soon with a lounge specifically for suite guests and Pinnacle members.
While I very much enjoy concierge lounge access, I have to tell you that during my Quantum of the Seas cruise earlier this month I thought to myself - if I were a suite guest and walked in this lounge to find this kind of crowd, I'd be a little less than pleased.
All of this, of course, is just my opinion....with the exception of the changes on Oasis of the Seas.