Yes, this is indeed the problem with scuba. I have talked abut that many times before. The vast majority of of instructors work for dive shops, and in theory, that is where the problem should be handled. Dive shop management should be monitoring their pool of instructors to ensure that they are acting within standards. Some shops do that. Most don't.Yet an issue as applied to scuba seems to be the re-calibration you mention. For the SAT, AP, etc, evaluation is done fairly centrally and based on a piece of paper. This mean gold-standard graded reference-essays can be inserted into the workflow of evaluators marking batches of current year students. So evaluator calibration drift (or laziness) can be easily detected and rectified.
The solution you advise would be outrageously expensive, calling for a massive increase in agency personnel to do that monitoring. If senior dive shop personnel would simply monitor instruction--as they should--it would be cheap and easy.
But it isn't going to happen.
I know this because as an educator, I participated both as a teacher and an administrator in the extremely thorough and outrageously expensive process of teacher evaluation in public schools. Every school is required by law to evaluate teachers and ensure that they are constantly improving in their craft. Sometimes it happens. Usually it doesn't. Almost every school has at least a couple terrible teachers despite this expensive and legally required system.
Years ago I was on a research team that investigated what was going on in 10 schools in a large school district. These 10 schools were doing a great job, with students outperforming what would normally be expected in view of their demographics. (Some were relatively low performing schools whose students should have been doing much worse.) In our investigation, every member of the team said we had never seen any school performing the way these were. We were highly impressed. We identified what they were doing differently from everyone else.
Please read what follows carefully.
When we were done, our results were presented to the school board, the administrator who presented them noted this irony: The good news was that everything we found coincided perfectly with another major research project--Effective Schools. The bad news was that everything we found coincided perfectly with another major research project--Effective Schools. In other words, the process for creating effective schools is well known already. In the schools we studied, the local leadership (principal) was aware of that research and was working to implement those concepts. For almost all of the rest of the schools in the district, local leadership was paying no attention to that and doing whatever they damned well pleased.
In other words, the tools to improving instruction are well known, and all that is required is for local leadership to implement those tools.