You can also get lvl 1 Zaibas by reducing your Daino by 1 level for 20 more hits (Zaibas lvl 1 with art, was something about 14256% fully invested) so the damage difference is only ~ 33264%.
I’ve done the calculation against Glacia (hard)s physical defense (408k) using my current average patk (36435). Zaibas lvl 15 would hit for a total of 1.532.027 damage (including Aukuras damage, calculating for 60% of the hits being criticals), Zaibas lvl 1 with lvl 15 Aukuras would hit for a total of 949.027 damage, which is ~62% of what lvl 15 deals.
It also depends on how many final damage boosts you have (e.g. crit amplifiers like Zalciai which isn’t included in the calculation and would shift the difference to up to ~88% more damage at lvl 15 compared to lvl 1 if you crit 60% of the time [which is highly unlikely, but it shall be mentioned for completions sake]) since they will only affect the base damage and not Aukuras.
So yeah, there is defintely an incentive to max Aukuras on endgame content, at least if you don’t have overgeared status with 45k+ patk/matk.
If you only consider field farming and CM/Division, it probably makes more sense to max Zaibas, considering you’re disabled like 30% of the time, thus cannot take advantage of Aukuras.
I wish they didn’t remove the 50% negative status ailment duration from Aukuras, it would come in handy at least there.
The question is also one of funding. Zaibas lvl 15 would need arts lvl 30 for maximum effectiveness while Aukuras only requires lvl 100 enhance attribute. I don’t have the funds to max another art, I can only afford Divine Stigma and Piety with what I have right now as free options since I missed a lot of free tomes and still have 2 more skills waiting for arts. I’ve also run out of AP because of the common attributes, so I probably won’t be maxing any Zaibas soon.