I think the difference is required knowledge. In Padi you could be a MSD through being a fishspotter, dpv driver, tea-bag diver, photographer and videographer, and although these specialties would have made you better at each of these things they may not have improved your general diving skills, e.g. Navigation, ability to dive deep safely, ability to know how to use lifting equipment or enter wrecks safely or perform more complex rescues.
If I understand correctly the NAUI/BSAC levels suggested above have more core components that you can't opt out of that improve your dive theory and skills thus making you a better alround diver.
Having said that if you pick the right specialties and instructor you may reach an equivalent level of skills, i.e. Nav, deep, eanx, S&R, night etc all add do your knowledge, confidence, theory and skills in a more general way.
Does this make sense ?
If I understand correctly the NAUI/BSAC levels suggested above have more core components that you can't opt out of that improve your dive theory and skills thus making you a better alround diver.
Having said that if you pick the right specialties and instructor you may reach an equivalent level of skills, i.e. Nav, deep, eanx, S&R, night etc all add do your knowledge, confidence, theory and skills in a more general way.
Does this make sense ?