Onhit item is never going to be balanced

It is basically a loop.

build On-hit items=rely on attackspeed and sustain damage=have to build tanky to survive long enough to do the sustain damage=not having enough damage

On-hit can never be viable unless paired with:

1. Broken champion kit(Pre-unreworked Kog'Maw)
2. Unbalanced item effect/stat(Sated devourer+Guinsoo)

both of which harms game balance tremendously.

The only times On-hit items are meta is when champions can build 1 or 2 onhit item then go full tank and still do carry level damage, thus being the so called "brusier" cough tank shyvana yi xin cough, only to have the items removed/nerfed/changed after the champions are nerfed heavily, leaving those champions in the dust.

oh wait, building 1 or 2 damage item then full tank and still do carry level damage? better nerf irelia.