I think the reverse exists as well. I think I am a much better test taker than average, and this has very clearly given me some advantages that come from the structure of exam-focused education. Exam taking is a skill and it's possible to be good at it, independent of the underlying knowledge. Of course knowing the material is still required.

However you are correct in noticing that there are an anomalously high number of "bad test takers" in the world. Many students are probably using this as a flimsy excuse for poor performance. Overall I think the phenomenon does exist.