Guba:Semantics is such fun...
The words "advanced" and "master" (as they apply to diving) are just about as subjective as the word "instructor". I've had the pleasure of having very qualified and conscientious instructors for all of my certifications. However, I've also come into contact with some instructors who can be defined as such in name only...they couldn't "instruct" their way out of the proverbial paper bag. In other words, they were very accomplished divers, and I have no doubt that they had impressive skills, but they couldn't translate those skills (or even the simple basics) to their students effectively. And for the record, the letters associated with their names included some other than P*A*D*I.
I suppose my point is that those who seek the Master Scuba cert need to do so because they want to improve some of their underwater practices and skills, not to laud it over and/or somehow impress others. After all, look at how it's earned...five specialty courses that might include photography, fish identification, naturalist practices, etc... It's not the same thing as learning about the types of embolisms or survival strategies. But then, it wasn't meant to be. Take the title (whether you think the word choice unfortunate or not) for what it was intended to be and not what we want to THINK it's supposed to mean, and leave it at that.
After all, "DiveMaster" means something entirely different than "master diver", and PADI makes no bones about that.
I have to disagree in that there is NOTHING at all subjective about what an instructor is. In the context of the dive industry, an instructor is one who is authorized by an agency to administer their courses and issue their certifications. The instructor may or may not be a good diver or a good instructor but they are, in fact, an instructor and it isn't the least bit subjective.
Maybe in contrast, What is a "Master Scuba diver" qualified to do? The title doesn't even tell you what specialties they have taken (thinking of PADI).
Now, if you really think that any of those courses did ANYTHING to improve skills or document that skills have been improved, you need to read the training standards for those courses. You may be surprised to find out how few of those courses require the student to do any more than survive the dives. That IS what makes the whole thing a JOKE. They aren'ty required to dive well in the OW course, AOR, rescue or in most of the specialty courses. They can crawl on the bottom through all of them and end up a "Master Scuba Diver". Nothing subjective about that either. It's in the training standards as plain as day.