I'm pretty sure that the only PADI classes required for the PADI Master Scuba Diver are the specialties. On the description for the OWD, AOW, and Rescue it says "or qualifying certifications."
And if that is the case that is inline with SDI and IANTD.
Yes, the PADI MSD cert requires OW, AOW, and Rescue as prereqs, but any or all three of those (if equivalent) can be from other agencies.
Only the five full Specialty classes must be PADI.
Plus 50 logged dives.
I'm hesitant to sign MSD papers (Yes, an instructor must sign your application) if the five specialties are "weak" (IMHO) and the 50 dives do not show a "breadth" of experience and challenges.
By "weak" I would include specialties that do not challenge the student underwater (like Nitrox), and/or do not really improve the diving perhaps because they have no dives (like Equipment), and/or do not provide new and useful knowledge (possibly Boat), and/or are "corrective" specialties for things you perhaps should have already gotten (like PPB). Fish ID or Underwater Naturalist can be trivial classes. or a serious look at fish identification or u/w life, respectively; if the latter I'm OK with it. The "high-end" specialties (IMHO) are things like Deep, Navigation, Search and Recovery, NIght, Cavern, Ice, Self-Reliant, Wreck.
By "breadth" I mean not all in a quarry, but rather a mixture of shore and boat dives, deep and shallow, colder and warmer, no and moderate currents, good and crappy viz, day and night, drift and stationary, just as a buddy-pair or following a guide....a little bit of everything.
And, as many have said, the quality of the training depends on the instructor, not the agency.