This is the PDGA's fault for not assessing the courses and giving a standard rating. Without that, the rating is all anecdotal. I can't tell you how many times I went to play at an out of town course and found an unplayable course with a 4.0-5.0 Udisc rating. The PDGA needs to get out there and standardize course ratings.
The PDGA tried that, years ago. Or a user-managed version of it. It had an incredibly long checklist list of criteria for users to complete, assigned a points value to each, and gave a course a rating.
If you looked at it, you would at least have information on every feature of a course.
The attempt was to be objective, but it merely pushed the subjectivity down ladder a rung or two. How much value should be placed on, say, bathrooms vs. scenery? No flexibility there. But how does a user rate the quality of teepads? That's subjective. How much extra to give to a course that's really unique? No way to account for it, but in the real world that's often the most attractive feature of the highest-regarded courses.
The end result was that nobody used it.
It would be impossible for the PDGA to "officially" rate courses -- too many courses, too many new ones. But even if they could, it would result in the opinions of a few people, by a standard set by a few people.
DGCR's system is pretty good, and probably as good as we can expect. It has the foundation of having started with a reasonable range of ratings (i.e., not a flood of 5.0s), and an average of opinions is a pretty good measure. You can filter for the ratings by people who have played a lot of courses, which is even better, though in reality it doesn't change the result very much.