the fact they can do 20+ Damage without much counter play is insane. not to mention they can do it twice. so if you are even slightly wounded you have a high chance to just lose to a Colo smacking you twice.
Suggested nerfs:
Make it only do the damage once, make it a sort of cross beam attack in the animations by merely having them play at once.
Second suggestion is to make it take twice as much to power it up. Sort of like Imbue Druid’s Hero Power.