An idea for mundo's Burning Agony

So is the master of HP,let's give a fast look to his abilities: P:scales with your hp Q:scales with enemy's hp E:scales with your current hp R:scales with your hp then we got W,it scales only with AP,a stat mundo doesn't really want to buy because only one spell will benefit from that,i know it gives "free" dps and tenacity but i think that changing the W scaling from AP to HP(something like a percentage of your HP as damage since mundo doesn't get damage while building HP) or maybe both will be something mundo would really benefit since now he's pretty weak and thematically makes sense at least to me,what do you guys think about it? PS:Sorry for some grammar mistakes