And Kes had MORE potential than Troi, so it's kind of silly to say that they had to dump Kes because it was "so hard" to write for her.
As I mentioned at the start of this thread, the actress playing Kes was also hard to write for, not just the character. Ms Lien is painfully shy in real life and, although she is capable of incredible performances on-screen (I liked her in the sitcom "Phenom" before I knew her on VOY), it could
be that some directors found it hard to communicate with her. Why she made public appearances at conventions when she is so shy is also hard to fathom; Jennifer Lien came to Australia and was so freaked out on stage that the audience thought she was under the influence of drugs. Some demanded their money back. Hence the many rumours that were racing around about her dismissal.
As we've heard with other actors, some characters inspire the staff writers to greatness. Others, for hundreds of reasons, don't work out the way the creators imagined they might at initial casting.
"Kind of silly", but the writers did find Kes a difficult character to write for. You can see them tinkering with the character every season (her powers, her appearance, the relationships with other characters), but nothing seemed to be working as well as they wanted. Seven of Nine, however, opened many wonderful opportunities for character building.