We run rather a lot more than 2500 instances at peak and a variety of instance types dependent on game mode. Our waste is on the order of 5-7% depending on the time of day -- we can run less waste on the downward slope of the demand curve for instance.
Aha, Fortnite. You guys will get discounts that we will never get, please keep that in mind.
Our waste was the inverse of yours, less waste on the upswing and more waste on the downswing, due to the long lived nature of our instances.
One instance takes roughly 1,000 players, but if you as a player decide to just keep playing, then we won't kick you out of the game for some hours. Some percentage of players will just continue playing as long as possible without matchmaking or map transfers.
We're also seeing some pretty compelling results from ARM based instances: https://www.wired.com/sponsored/story/changing-the-game/