Aphelios 's crazy Severum (main hand) + Crescendum (off hand) combo

So basically our edgy boy has a crazy ass combo that uses the active Q for Severum to stack Crescendum in offhand to absurd levels of damage. Once you exhaust Severum's ammo you swap Crescendum to main hand and dump all of your stacks while refreshing them in combat until Crescendum runs out. I feel like this isnt super busted, its kinda like Kalista stacking 1000 spears on gromp and q'ing someone to oneshot them.