Here is the definition:
1. of only ordinary or moderate quality; neither good nor bad; barely adequate.
Here is the problem:
How does one define quality?? Quality to one is trash to another. McDonalds is a fast food phenomen with people spending billions there annually. Even though I view the product as very low quality, most other don't and so they consume. Its all relative.
For you bay area boys, if you play courses like Cypress, Spylgass, Pebble, Pasatiempo, etc, day in and day out, then you make think a course like Cinnabar Hills is Medicore and barely adequate. But if you usually play shoddy, ragtag munis with flat greens, soggy fairways, and no bunkers, then playing Cinnabar Hills would seem to be a nice, very well done and exceptional course.
Whether or not one views a course as "Mired in mediocrity" or not, in large part depends on thier viewpoint.