I think you might be overstating the importance of the SMB a bit....there was no such thing in the 60's, 70's, 80's, and most had not seen these in the 90's.
While common today, divers were not "dying like flies" in the preceding 4 decades, due to lack of the smb.
Personally, I think it is a simple skill anyone should be able to teach themselves, if they see some other diver do it effectively, or if they watch a youtube video of how to do it. The real issue is do you have good neutral buoyancy in mid-water--that is the real skill to learn--to be taught by SSI or PADI, or NAUI, GUE or whoever. Once being stable at 20 feet is simple, playing around with a reel and a float really has no challenge to it. The problem is that too many classes never teach the students to hold a depth like 20 feet without the diver having wild up and down swings of depth.