DFT has to be a little better for DoT and AOE. and keystones in general
it has to be at least a choice. DoT for single target is fine (only on jhin). I know rumble picks it up sometimes and few other mages. but I never took even 100 damage from it in a long ass trade.
just buff it a little for AoE at least or make it do variable amount of duration based on how long the DoT is. it just sucks. I never seen anyone die from DFT except from Jhin.
and second of all. when are you gonna change what and how keystones are procced. what is considered a spell and what isn't is completely fucked in this game. there is no concrete anything. I'd love if darius passive procced spells so I can use dft same way Jhin can use it I mean it should be an option.
Remember the introduction of keystones "you make a choice depending on what you want to do" what we got
" you don't make a choice you pick depending on what champion you are picking".