Becoming a Drill is one of the best career accelerants available in a peacetime Army. DSS isn't easy, it's not for everyone. It's a real test of "how bad do you want it" sort of thing. The Drill Sergeant class I just saw graduate from Jackson in SEP had room for 80, enrolled 63 and graduated 38. That tells you how difficult that school can be. I've been told it's at least as difficult as Ranger School. Don't know. I'm not a Ranger. I can tell you the cow's brown on this side, though, because I AM a Drill Sergeant (to the bone!)
As I recall, most people wash out of DSS because of the academics; a fair few from PT.
Once you've got that hat and badge, there's no question in anyone's mind what you do for a living. Turning BCT people into Soldiers is a challenge with long hours. However, when you stand in front of that platoon on day 63 and think back to what they were like on Zero Day, when you know you taught that Private who was scared to death of a rifle and s/he qualified....ain't no better feeling noplace.