Potential exploit with Vaal Clarity and Archmage Support with persistent spells

I've been having a lot of fun with the new Archmage support, to help supplement the increased mana cost I run a level 1 clarity (which happened to be Vaal'd).

Last night I was in a bit of a bind. I ended up in a no regen map, on my last portal, and with no flask charges. So I caved and actually used Vaal Clarity expecting my damage to tank to almost nothing. Thing is it didn't.

Once I had my storm brands attacking they seemed to be doing normal damage. Granted it's very difficult to see the difference in damage against trash mobs, but when the difference is supposed to be 18k tooltip vs 120k tooltip you would think it would be tougher to kill them (Note, this was a tier 15 map for reference).

I don't know for certain if the interaction is occurring like this, if this interaction is intended, or even if its exclusive to persistent spells such as storm brand and not others like ball lightning or storm call.

Figured you guys might want to know.