Though I don't think GULC is overrated, I think the thought goes something like this.
The US News rankings are an estimation of some real, hard-to-attain ordinal rank of law schools. This assumes that the US News is not the real value, but a pointer (or not a pointer) to some ontologically significant, unknown value.
Your analogy does not work because value, when referring to stock, is defined in terms of how much two parties are willing to buy and sell it for (or something like that). With the US News rankings, and somebody saying X school is overrated, the definition of value is not based on the US News rankings, but that real ordinal rank I spoke of above.