In my opinion, the value of a good judge sheet is feedback from an outsider who knows at least a little bit about beer. I don't think teaching how to brew is necessary. Especially with the volume of great info available. For example, it should be a given how to avoid oxidation... so, "faint cardboard flavor, slight oxidation" is good enough. I can figure out where it's coming from.
Not all homebrewers are so educated on off-flavors and how to avoid/mitigate them. Your example of oxidization is a great one. Some homebrewers may not realize that this is even an off-flavor. There is a whole lot of ugly baby syndrome out there when it comes to homebrewers. Some homebrewers may not realize that could be the result of their process - such as not carefully bottling from the keg because they're not detecting it in what they're drinking at home (This happened to me once). Oxidation in varying degrees of severity is probably the most common off-flavor in entries to competitions.
Ray Daniels calls the ugly baby syndrome as cellar blindness, as in that beer was excellent in my basement and I entered it. I have been guilty of that, and now get a second opinion from my wife, who has a better palete.
Agree on excellent beer being degraded in the bottling process. One of my issues was creating diacetyl in a Pilsner through rushed bottling. Diacetyl was in the control bottle I had when reading the score sheet. Had a sample from the keg, and it was clean.