For years divers were taught to use the drysuit for buoyancy and the BC as a backup. There are two issues with this procedure, especially for a doubles/wing configuration:First you are training divers to behave differently when in a drysuit. (When wet use BC, when dry use suit.) During an emergency, you do not want to have to consider "am I wet or dry". You want to have the same emergency procedure.
Second, it is less stable. If you have heavy tanks above you and extra gas in your drysuit, then you are unbalanced. Like balancing a on a beach ball. Also, that gas is not stable in the suit. Any extra gas (beyond that used to remove squeeze) will move to the highest point in the suit.
On the other hand, consider only adding gas to the suit on the way down the anchor line, and just enough to remove squeeze. Now use the wing to control buoyancy, just as you would do if you were wet. You now vent the wing as you use the gas in the tanks, just as you would when wet. You are now using the same procedures wet or dry.
Also you now have gas (buoyancy) around the tanks, not under them (this applies to wings and back inflation only). The gas in the suit can not move around as much since your undergarment has it trapped. Both add up to a more stable configuration.
I'm not saying this is the right way to do it, or that using the suit only is wrong. I'm just saying that this is the thinking behind the way it is currently being taught. I personally find it more stable, but that's just me (in a BP/wing configuration).