Normally it is 5 stacks of 8% power that only affects melee damage. For Vet Shovels and Taxes, it is 5 stacks of 10% that affects all of the damage you do while the weapon is out.
I’ve been using Decimator and Headtaker together, with Warp Splitting the cleave issue in hordes is hardly apparent unless Elite enemies with heavy hitmass are present in the horde. Taxe VII with H1, L2 and the push attack into heavies are my go to horde attacks.
Will have to try the Bromentum with Decimator. I was skeptical of Decimator at first, but like you said it builds stacks very fast on Taxe during horde events and it helps against bosses as well.
As for that bug, maybe I’ll try it on a Soulblaze build. It’s crazy that any melee weapon Blessings like Uncanny or this one carry over to DoTs at all.