Dark Harvest having an actual Feast or famine effect and being a late game rune not an all game rune

Dark harvest is supposed to have the nasus q stack or the veigar passive fantasy from my feel, and the current problem with dark harvest is its just a burst rune. i think the biggest issue with dark harvest is its base damage and lack of feast or famine most of the time a character with 4 DH stacks feels like they do more dmg if they're behind then if they had electrocute. the next problem is the fact that it procs off of any dmg. Now for my solution i propose a few things

1. Dark Harvest doesnt need base damage
2. Needs to scale better not be good at all points of the game you should be punished early rewarded later
3. needs more strict procing rules so the answer to all of this is this: Is you proc a burst of dmg when you strike an enemy with a move that does X amount of Dmg ( im gonna say 50 for now for ease) when they are below 50 %HP for DH stacks(maybe times 2 or 3 mostly here for example) + 02% +01% per stack Total AD +02% AP + 01% AP per stack Adaptive dmg. Gain one stack everytime you proc it and one stack for Every champion KILL. Cool down 60s - 1s per stack (caps at 20 or 15 seconds) Notice that it doesn't reset in team fights and only get bonus stacks for kills not take downs so it cant be abused as much by supports or tank junglers I believe that this is the correct way to go for an infinite scaling rune which is what i believe was the goal (correct me if im wrong) this is not the only way i thought of maybe it requires X amount of stacks before it even does dmg say 5-10. but again i think this is the path that the rune should take and be the feast famine its supposed to be. If you would like to add to this or tell me Dark Harvest is balanced please let me know

If someone will give me a tldr that would be swell, thanks!