No offense, but if you sailed before STCW was instituted then you also sailed before ISM was ubiquitous throughout the industry. No one who is sailing as Master wants or needs extra work thrown on their desk to further evaluate people beyond what is already a full dance card of endless paperwork.
I am constantly assessing crew performance for the main purpose of making sure the ship is being run correctly and safely. You are correct that on the job training is critical but @jbtam99 is correct that some people are out here looking for an easy sign off with no real mastery of the job being assessed. Hell, some are struggling with the job they already have so why the hell would I want to help them up the ladder?
The classes should be the norm.