If it were to made mandatory, it should be part of the Advanced certification. Divers in initial certification are already in information overload just learning the basics such as breathing underwater, mask clearing and out of air.. Trying to get them to demonstrate "peak performance bouyancy" is asking way too much for someone who has just been in a pool twice before. However, I bellieve bouyancy should be a mandatory part for you to be called "advanced." Let’s face it.. The PADI "advanced" rating is far from that. I have always had a problem with the "advanced" rating. But, if they made PPB part of the course, it would help in giving you skills you could actually use at being a better diver.. Much more than "photo" or some of the other specialty dives you can do in your Advanced cert.
As for the newly certified diver that mastered his own bouyancy. Good on you. I think every diver should work on their bouyancy and get it down. However, in the sense of getting your AOW, you’re not paying the dive shop for the single specialty. You’re paying the dive shop for the advanced cert which includes 5 dives. If you have PPB already mastered, then you’ll breeze through that portion of the dives. But, you will also be under the eyes of an instructor and that can help you with whatever you might think is "mastered" yet it may not be quite right. Just my train of thought on it..