Cat D at one point was assigned to pilots who were clearly lacking in skills. You could watch how they operate and it was clear. Now it’s assigned based on a multitude of reasons. Some even being political.
If a pilot who has spent 13-14 years flying the line and passing all their checks. There is no reason to not assign them a course. To not, is a failure of the training system.
I find that the enforcement of what is “standard” is very subjective. One checker gives you a 4 and another gives you a 2. I am frequently frustrated by this. Having flown for a few Airlines. This is the first one that I consistently ask, what the hell do they want?