I feel we've lost sight on what Dark Harvest was in the first place

Dark harvest was bonus damage on a single auto attack.

It offered easier activation compared to the 3 hit requirement of electrocute, and more reliable application compared to meteor.

The tradeoff was that it generated weaker damage during the early game.

Changing DH to apply to all damage dealing abilities radically improved it's ease of application as abilities often have greater range than auto attacks and can sometimes apply to multiple targets simultaneously (see karthus)

Before nerfing its damage to deathfire touch 2.0, why not dial DH back to auto attacks only?

Keep the other changes such as the backloaded damage / removal of pve farm scaling, and see how it feels as it was meant to be. A single target, around 550 range auto attack enhancer that's weak early and scales into the final 3rd of the game.