Alright, you challenged me to it, so let me see what I can dig up that meets some of your criteria. This is an assortment of non-standard MLs, to varying degrees of your required attitudes, with most focus on being nobility or adjacent without being a prince or a Duke.
Ascendance of a Bookworm (HIGHLY recommend the LNs)
The Lady Likes a Nerd over Princes
No More Princes (?)
I Woke Up as the Ugly Duckling
The Boomerang Duke (for his personality I swear)
Straight to the Red Carpet
On Her 94th Reincarnation, the Villainess became the Heroine
Madougushi Dahlia wa Utsumukanai (sort of maybe)
I’m the Villainess, so I’m Taming the Final Boss
The Villainess wants to Marry a Commoner
The Goddess of Healing
Primitive Boyfriend
Mahou Tsukai to Koi no Biyaku
My Ray of Hope
Tensei Shite Yandere Kouryaku Taishou Chara to Shujuu Kankei ni Natta Kekka
I can look for more if you want, but I’m literally sitting here with my lunch getting cold. XD
So imma jus add this to my reading list thanks ╮(￣▽￣)╭ these better be good (=・ω・=)
I try not to recommend things I don’t have a good opinion of. XD there’s only one that’s super weird, I think, and that’s Primitive Boyfriend. But it’s weirdly Otomege-adjacent and super non-standard ML so I went ahead and added it.
Ascendance of a Bookworm is one of your closest matches I think. Priest with bad attitude and manners as a main character for a good bulk of a 33 novel series. I love Ferdinand. He’s such a grumpy cat.
Though both of these are ones that start when they are children.
This one ml has like holy power
The Monster Duchess and Contract Princess
Surviving as an Illegitimate Princess-
This one her dad is a holy knight that doesn't acknowledge her because that means he broke his vow of celibacy.
This one he is kinda like a pope but also ruler of his own place
Daughter of the Emperor
This one I recommend the most has a type of priest only as a second ML, but the plot is different because main character is a siren.
I didn't put the name of the last one Becoming The Villain's Family
everything about isaac is just perfect for me PLEAZEEE I WANT MORE PRIESTS LOVE INTEREST PLEASE GIVE ME MORE OF THEM (i do not have a kink for priests. i am just tired of the dukes and crown princes being the male lead, please let me taste something new)
also because isaac looks and acts so much like romano from hetalia lmfao. i am pure cringe but i will never forget my love for romano so this is the best manhwa for me at the moment (unless anyone suggests another manhwa with brown hair, green eyed male leads who has a bad temper and etiquette but is a softie deep inside)