GUE don't seem to have a problem.
Actually they do. I have posted several times about a fundamentals class I witnessed in Egypt and it got the attention of GUE who wanted me to tell them the instructor's name.
About mastery
Mastery is defined as being able to perform a skill repeatedly, correctly and comfortably. In the context of the OP's post, it's pretty clear that the student wasn't able to perform skills in this manner.
"Perfectly" is not part of that definition and that's the slippery slope. "perfect" execution of a skill is hard to define and it's different depending on how much experience the diver has.. This is just a fact of life so complaining about it being like this doesn't make much sense.
Nevertheless, all instructors are trained to initially understand what "good enough" looks like. You were taught like that. So was I, so was John and so were the unimaginable train wrecks of instructors that people complain about on the interwebs.
However, almost immediately after newly certified instructors start teaching they start to "drift". Some instructors become more strict than PADI (or any agency, since they all work the same way) really trained them for and some become sloppier. Over time this drift can become severe. PADI is the only agency I know of that invests much effort into any kind of QA that regularly identifies and "re-calibrates" the "train wrecks". Other agencies do work on QA but not in the same way. GUE, for example, as I alluded to above seems happy to do QA based upon hearsay. Other agencies probably do other things.
On the flip side, instructors who become severely de-calibrated on the stricter end of the scale can cause problems too by potentially putting students at risk by requiring learning skills that are unrealistic, or learning skills in an unrealistic manner. As far as I know, most agencies don't seem to actively weed out these instructors but I've read some stories on the internet that makes me think that the problems can be real. It also seems clear that students can get confronted with escalating costs for things that they have already learned well enough for the agency, but not for the instructor. If this is what the student want's fine, but sometimes instructor's perfectionism can get in the way of being fair.
R..