Well, it sounds like you did everything right. I guess the only other thing you could try would be to open up and do the toothpick test at 3.5-4.0 hours instead of 4.5.
I usually do St Louis cut ribs that I don't check until 5.5-6.0 so I am definitely not the expert on Baby Backs. Although, my next set of ribs are going to be Baby Backs from Sam's Club though.
Regarding the water in the pan, mine usually isn't very depleted either. I think that is pretty normal.
Let us know how your next smoke with the 2-2-1 goes. For me, I have such good luck with the no peak that the thought of doing 2-2-1, doesn't excite me at all.