All this means is those mil pilots scored high enough on the app board that they are competitive with the current group of interview selects. Delta is just not interviewing mil guys with commitments a long way out like they used to. e.g. One guy I interviewed with in 2013 was not available for almost a year. The company didn't mind having a protracted pool then...apparently they don't do that now.
I agree that the current build up of a pool is temporary. It'll thin out quickly once the training department goes back to normal throughput. Sucks for the guys caught in the pool who are anxious to move on...