I see this in the Irish trad and Old-Time scenes all the time. A lot of sessions have the one sweet guy or gal who everybody likes, but who is so bad, it's an empirically measurable fact. There's one Houston drummer whose technique for holding her stick is so bad, her 2nd beat each measure falls at random every time. You could take a recording in Audacity, put in the tic marks, and it would be glaringly obvious. I've encountered many musicians with no rhythmic sense and others with no sense of pitch to speak of. I've also encountered musicians who are very competent in one genre, but have not enough clue to know they're clueless in Irish trad. This weekend, I was playing with a wonderfully competent old time player who had no clue the emphasized beats in Irish trad fall on the downbeat and not on every upbeat. Doing the latter obliterates the occasional deviation that can add playful (purposeful) changes to the rhythm. It's like showing a Picasso blue period painting under a blue floodlight.

The lesson here: One can be very good in one area, but still very clueless in another, even a closely related one!