On Feb 1 I also got my D360 for the fourth year in a row. I was a bit worried because my spend dropped a lot last year because I had very little international travel last year.
I would expect that the 360 membership numbers must be at least as high as CK or GS.
Personally to me the whole program has been a disappointment. The benefits are nowhere near as good as GS, and even the white glove service is not close to the level I used to get from AA as a Concierge Key member. Plus with the devaluation and decontenting of the Diamond program, you are now less likely to be upgraded as a Diamond 360 than as an Exec Plat at AA.
I wish Atlanta had a second hub airline TBH.