I didn't find a particular shortage in elevators when I was on Freedom of the Seas. Sure, if everyone is leaving the showroom at the same time, there could be crowds around some elevators, but with 3,000 passengers, that's to be expected.
The only problem I ran into with the elevators was debarkation after the cruise was over. I was sitting on the Promenade Deck, waiting to be let off the ship, and all the elevators coming from higher floors were full by the time they stopped on that floor. Eventually I took an elevator up and then down again...