I dive with a drysuit when I’m diving local (Central Pennsylvania) cold water sites. Been diving drysuits for quite a while. When I am on the surface I use my BCD for floatation. As I submerge, I vent all air from my BCD and use my Drysuit as my primary buoyancy control. When I am coming back up, I do a safety stop at about 15ft, during which I vent all air out of my drysuit and switch back to my BCD. I realize that most drysuit divers wait until they are completely on the surface before going back to their BCD for buoyancy, but I figure I have to wait at the safety stop for a while so I might as well make the most of it.
I have found that if I need more buoyancy than my drysuit can provide, while I am at depth, then I am overweighted, and I adjust my weights accordingly.
What it comes down to is that "Yes" I use my drysuit as my "Primary" buoyancy control during the dive , and I use my BCD while on the surface.
Although I am not the most experienced diver in the group, I can say that this technique has served me well. I have yet to make a trip to the hospital because of it, nor do I feal particularly like an "Idoit".