He was a REAL BRAT in TNG.
I think his grandparents must have been incompetent because Worf was the only child that came out okay and he was an alien...
Worf was found by Sergei when Sergei was a young man and had the energy to raise him along with Helena.
Alexander was sent to Sergei & Helena when both were in their twilight years. Try handling a Klingon child then
, and you'll see why they sent him back to Worf.
EDIT: If anything, I think that Klingon culture
failed him, first by not taking him in after his mother died, and forcing him to live with his grandparents due to its rules about discommodation. Alexander also has to share some of the blame by not doing as his daddy said and go off to a Klingon school to learn the male coming of age rites and the other things that make a Klingon a Klingon.