Well lets agree to disagree. I feel differently. If there is a course regardless of how horrible it is, I would give it a .5 just for its simple existence. Maybe the course just needs some love and attention. Maybe it would be good for little kids. Maybe there isn't another course of any quality for many miles. If the baskets at a course are used as trash bins or are in a horrible state of repair including some missing now becomes an object course. Its all perspective.
And on the flip side, 5 rated courses... I take more into consideration than just how it plays. But then I'm an average "rec" player. I look at the bigger picture than just the technical aspects of the game. And a course with no place to "pee pee" except the woods is not a 5 because there is something I would do to improve it.
If I'm going out of town and I'm looking to play a round on my trip I look at reviews. I'm not going to waste my time on a course with anything less than a 2 rating unless that's all to be had in that area. I read all the reviews available for a course new to me. If this course is rated a 5 but there are no amenities I might choose a 4 rated course with the things I like in a course.
I also "read into" what the reviewer says. Some people are overly effusive with praise for things and that immediately knocks their rating in my mind. Then some others are disc golf snobs who put down everything but the most technically demanding courses, and this comes through in their reviews so I bump the number in my head a bit.
Unfortunately like almost everything else in this sport, there is no real consistency.
A perfect case in point locally is Chestnut Ridge. I played it once as a noob. I did not rate it. If I were to rate it today based on what I know about the sport it might only get a 2.5 from me. while several othrs rated it as high as 4.5. I can't fathom why. Signs were inaccurate, it is difficult to negotiate without a map and even then it isn't that easy for a noob. And if my memory serves correctly it was at one time considered a Top Ten course. Of the course I've played it would be at the bottom of the list.