Based this list on their current capabilities.
Andrius : God of Blizzards. Canditate for Anemo Archon after Decarabian’s death. Covered the entire region of Mond in a blizzard for an unknown amount of time (a few centuries at the very least imo). He is weakened at the moment as he doesn’t have his original body anymore, but that can be solved as soon as he finds a vessel that can handle his entire power.
Dvalin : An elemental dragon, which already puts him higher than most. Was able to defeat Durin with assistance from Barbatos. Imo, he and Andrius are the strongest beings alive in Mond.
Decarabian : God of Storms. Previous Anemo Archon (may be mistranslation). Protected his people from Andrius’ assault for an unknown amount of time(a few centuries at the very least imo). Also created his city by only using his powers. Had access to multiple elements (Anemo and Cryo at the very least, like Andrius).
Bloodstained Knight : Part of the Cataclysm Gang. Disciple of the rival of Arundolyn, Wolf Pup Rostam. Went on a monster killing spree which ended in Khaenri’ah where he joins the Abyss.
Crimson Witch : Lover of Rostam. Became an arsonist after his death. Bruned all sorts of monsters. Now, she is apparently a Fatui Harbinger.
Arundolyn : Lion of the Light. One of the strongest people of his generation. He dual-wielded greatswords and longswords in battle, a style which has become extinct now. He was strong enough that people said that he would be the one to slay Durin.
Rostam : Wolf Pup. Former leader of a secrect info network. Rival of Arundolyn. Died in an expedition to presumably Khaenri’ah.
Varka : Grand Master of Knights of Favonis. Knight of Boreas. Titan of Mond (by Childe). Defeated Eula, who is on par with Jean. Goes on dangerous expeditions on a regular basis.
Albedo : The only reason he is here is because he has the capability of destroying Mondstat.
Lisa : Most powerful witch in centuries. Studied at Sumeru Academia. She is lazy, so she holds back a lot.
AA : (Everyone is nearly on the same level)
Members of the Wandere’s Troupe : Led an rebellion against the Aristocrats. They failed, but each member of the Troupe was powerful in their own right.
Jean : Lion of the South. Dandelion Knight (more like dandelion thighs). Helped us in calming Dvalin down. Spars and ties with Eula on a regular basis.
Diluc : Darknight Hero. Former Delusion user. Orphan. Defeats Abyss Mages (canonically very difficult opponents) like they are slimes.
Kaeya : Cavalry Captain without a cavalry. Last hope of Khaenri’ah. Tied with Diluc when he did not have a vision. Relies on manipulation and hides a lot of his actual capabilities, so he might possibly be in S-tier.
Eula : Spindrift Knight. Caption of the Recon company. Born Lawrence. Spars with Jean and ties with her on a regular basis. Has sparred with Varka before, but she got bodied.
Barbatos : Anemo Archon. Has suffered a significant decrease in power. From terraforming Mond, to scaring away Ursa, to only being able to assist Dvalin in fighting Durin, and to finally getting bodied by Signora.
Rosaria : Nun at the Church of Barsibato. Literal backstabber. Defeats low-level thugs on a nightly basis.
Amber : (Only) Outrider of the Knights of Favonius. Very skilled, but she lacks in power. A few years and she will be higher up in the list.
B : (Everyone is nearly on the same level)
Noelle : Saitama of Genshin. The only reason she is not higher up is because she lacks combat experience and possibly, skills.
Fischl : Delusional child. One of the, if not the, top investigators of Mond Adventurer’s Guild.
Bennet : Child forsaken by the world. An adventurer who has had multiple near-death experiences. A jack of all trades. Has the potential to become very strong in the future.
Klee : Spark Knight. Has a penchant for causing destruction, just like her mother. Still a child, so she has no combat experience and neither skills.
Civilians : Barbara, Diona.
Not enough information:
Aristocracy Gang : Eberhart, Parsifal, etc.
Stanley : Greatest adventurer of Mond. Died in Mare Javari. Can not make any estimates until we get more info about Mare Jivari and the monsters residing in it.
Alice : Mother of Klee. Adventurer of the same renown as Stanley. Outlander. Author of Teyvat Travel Guide. Can’t make any estimates until we get more lore about her.
Debatable Cases :
Vennessa : Lionfang Knight. Dandelion Knight. Falcon of the West. Defeated Eberhart’s gladiator, who was the undefeated champion of the arena. Didn’t die at Ursa’s hands, which more than what a certain red-headed father could do. Originally, I put her in SS-tier, but she is currently stuck as a falcon, so it is not clear how powerful she currently is.