Shouldn't it be "monkhood" rather than "priesthood"? We are dealing with Buddhism after all.
@A-tan As ridiculous as Yoriichi is, I don't think this chapter particularly contradicted anything. It just showed us how high up the sky is.
Recall that the reason the derivative Breaths exist: though hunters may train themselves in the main Breaths (eg Water, Fire, Lightning), whether it's because of their physique or other factors, not everyone is capable of mastering the main Breaths to their limits. So while we have people like Urokodaki and Giyuu who master the Breath of Water, we have people like Kanae, Shinobu, Kanao and Iguro who use Water derivatives like Flower, Insect and Snake.
In that sense, it makes sense why the 5 main Breaths are derivatives (or "inferior versions", to use Rengoku's dad's words) of the Breath of the Sun: it's a style so overpowered that so few were able to replicate it like the original swordsmen did.
In saying that, I don't blame you for being ticked at the lore in this. Born with a Mark, access to the See-Through World and natural talent for the sword? The heavens were utterly biased towards this guy, he ticks me off too. The lore however is delicious.
Also, keep in mind that this was the guy who established the modus operandi for demon hunting (the Breaths) and probably helped the founders of the Blacksmith Village with the development of the Nichirin Blades.
If anything, I really sympathised with Michikatsu (UM1) here. His envy is his downfall, but he's the actual hardworker here.
It also makes sense now, why Rengoku's dad was so utterly incensed with the Breath of the Sun: if someone and something was so far beyond what mere mortals can strive for still failed to end Muzan, what hope do they have?