Over all I agree with the take that clemency + guidance is usually my go-to combo to make early primus fights sustainable.
Though I think the Issue is not the essence combo itself but the ways sustainability works. Characters cannot solo sustain with just healing or life steal since characters that would profit from it are usually in the realm of getting one shot anyways. Furthermore just using healing doesn't work since the last world and primus's last phase completely negates healing with the 'healing reduced'-mechanic. Players basically HAVE to stack shields in order to survive on a tiny platform that makes dodging large area attacks near impossible.
Instead of adjusting those two essences, they either have to change the healing reduced mechanic and allow debuffs to be cleansed some way shape or form, permanently. Since the actual debuff cleansing right now would only lead to primus re-applying the debuff all together, or give players other options to solo sustain a fight with damage dealing travelers. Shields are a must have at this point of time unless you out damage the boss entirely and skip the doomsday phase. Dodging just isn't rewarding when you can tank the damage with a 100k+ shield, armor isn't rewarding unless you heavily invest in it through ng+ runs, so what is left?
The game lacks self sustainability options, obviously players choose the only one available.