Because DoT and pet defense and attack are specific values they become increasingly underpowered as more and more powerful endgame content and gear is added.

Since the additional content generally includes new more powerful gear which increase damage and survivability of most classes/skills yet completely ignores Mystics pets and all DoT skills these skills become more and more useless. Which is particularly bad as theses skills are relatively underpowered to begin with.

My suggestions are something like:
DoT Skills
damage = ( 1 + ( attack / 6000 ) ) * base damage

Pet Skills
damage = ( 1 + ( attack (character) / 6000 ) ) * base damage (pet)
defense = ( 1 + ( defense (character) / 3000 ) ) * base damage (pet)

This has little to no impact at low levels but allows these skills to scale up in endgame as other skills do. This mechanic functions similar to the heal modifier for priests and mystics which is another viable alternative for the pet skills.