The buffs part refers to things such as the Wonderous Physic, consumables and spells which as Golden Vow.
This boss aside from a few strange hitboxes and the horse roar is actually pretty decent.
He does also sometimes just loop a single combo string many times in a row, I think I had him loop the same combo string about ten times in a row in a previous attempt and only went into phase 2 with about 40% HP remaining.
I'm not sure how long the no blessings part will last since I don't really like a lot of the bosses in this DLC and this damage is quite low even compared to the amount of damage you do against the late game bosses in the base game; This damage looks comparable to no talismans, no buffs damage against the late base game bosses and this is a pretty early DLC boss.
I did run through as much of the DLC as I could without fighting any bosses in a previous NG+ cycle grabbing fragments and in combination with this current NG+ cycle I do have 50 fragments which is the amount you need to max out your blessings so I may use those if things get a bit too ridiculous and I'll just backup my save before doing so just in case I ever want to try doing fights without any blessings in the future.