Is Duskblade Setting up a Bad Precedent?

So, AD and armour penetration, now called lethality have been two sides of a very easy to understand coin for a long time. AD increases the raw damage you do, armour penetration does not increase the actual damage values your attacks and abilities do, but they increase your damage output because they reduce how much of your damage is mitigated. Simple idea.

Duskblade sets a bit of a worrying precedent though. Currently Duskblade's passive rewards the player with some on-hit damage. This damage scales with lethality itself, it's a 200% lethality damage ratio. Duskblade's passive deals true damage meaning that it's damage doesn't actually benefit from penetration it already ignores armour, but lethality will increase its damage value. However, the mere existence of a lethality damage ratio creates the possibility for more of them in the future. Down the road we may see Lethality damage ratios native to the kits of new champions. We may see them on abilities which do physical damage, simultaneously increasing the damage said ability does while also reducing how much the enemy can motivate said damage, doubling down on the efficiency of armour pen as a stat. Especially if it happens to be on a skill which has a %hp damage component, which are only mitigated by resistances and not health pools.

What do you guys think should we be concerned? Or do you think Riot has the foresight and restraint not to ever let this mechanic evolve beyond Duskblade?