It's understandable though. Why would you want someone mediocre doing a job when you could have someone with excellent intelligence?
Unless you were worried that they would do the job too well and usurp you.
Also, this sometimes works in opposite ways. For example, when my uncle was looking for someone to work in his warehouse, he rejected the more highly qualified people and went for people with fewer qualifications and a worse history, to give them a chance to do something positive.
Also, 1 and 2 are fine. 3 could be ok in some circumstances. 4 is not ok and 5 is racist. xo