It's more than just PADI. NAUI teaches using the dysuit as the primary source of buoyancy. Though not a training agency, DAN is in favor of the drysuit as the buoyancy source:
Medical Considerations for Drysuit Divers
When you are doing single tank stuff with proper weighting, the amount of air needed to "remove the squeeze" and the amount of air needed to maintain buoyancy seeme like they are about the same.
Nobody advocates having a large air bubble in the suit... NAUI, PADI, DAN, etc all suggest avoiding that by having proper weighting.
When having enough air to eliminate the squeeze gets you neutral and you can use lungs to adjust from there - both the "use BC" camp and the "use dysuit" camp are in agreement.
The disagreement seems to come when the amount of air needed to maintain buoyancy would require a lot of air in the suit. PADI, NAUI, etc would say: "Well... don't do that. eliminate weight" and there are obviously cases where that's not feasible so you have the choice of puffing up like the michelin man or using your BC.
Most on here advocate that BC is safer than being a michelin main in a drysuit because that large air bubble moving around a drysuit requires more thought and effort than maintaining two air bubbles.