I agree with you about irrelevant questions, and out of the dozen or so coding quizzes I've done over the past several years, mostly with start up companies, those are unfortunately usually what I got. One company was advertising for a front end role and, sensibly enough, asked front end-related questions - that was the exception.

And the thought that quizzes provide a fair point of comparison comes across to me as putting process ahead of substance. Interviewing isn't meant to be fair to everyone - only one person gets the job, after all - so it's not like handing out cookies and stickers in middle school. It's meant to see, in part, whether the person is capable of generating working code. If you have a person who can provide samples to prove it, requiring an artificial quiz really is a slap in the face to a lot of good candidates.