The Problem With Dark Harvest is Not its Damage

It's how easy it is for players to proc it as a coordinated team on one target.

And then they can do so again on the next with its low cooldown.

Rather than nerf its damage, Dark Harvest could easily be readjusted that it only procs for champions who have recently damaged the target. And if the takedown CD was changed to a reduced CD on a kill and NOT a takedown then it would eliminate the problem of 3-5 players spamming it on all enemy champions in any given team fight.