Of course they could have not written him into DS9 at all. I had no problem with a young Klingon who wasn't perfect. No young person should be well-rounded. On the whole they dealt with the problems of young people quite well in DS9. They were all, with the exception of Jake, rebelling against their parents to a greater or lesser degree. What's to say Alexander didn't get his youthful need to belong to the military off his chest and go on to great things. All he ever did was what most unhappy boys do: whatever is most likely to enrage his father.