I think it really comes down to the type of diving that you are doing.
For me, with a single tank, recreational diving, the air added to my suit for squeeze solves about 99% of bouyancy issues at depth. The situations are rare that I need more air in my BCD/Wing for bouyancy.
For me with doubles or stage bottles, I don't want to add that much air to my suit for bouyancy. I stick with the amount needed for squeeze to the suit and the balance to the BCD/Wing.
Remember that the scope of the PADI drysuit specailty/adventure dive, is related to the single tank, recreation diving. If you are properly weighted, then the air to your suit for squeeze should take care of most of your bouyancy issues. Once you move on to other realms of diving where more bouyancy is required, you'll want to use other sources to provide that bouyancy instead of relying just on your drysuit.