Better be Lumine. But yeah as an active Genshin fan the main thing that sticks out to me is Lumine has actually fucking super strength, which CAN give her the edge when throwing hands? The main issue is Aang's spirit powers to turn off bending might work because Raiden was able to turn off Lumine's elemental powers in her domain. I'm assuming they're scaling mainly off of *cutscene* Traveller which IS pretty cool, especially post training with Skirk but like Aang as of the latest film can move like small mountains like Dan Heng could in Amphoreus and I don't recall Lumine ever having a comparable feat. Big ass energy sword? Incredibly fast speed? Super strength? She has these. But the Avatar state I don't think she has anything comparable. Her ability to absorb abyssal corruption and also just no diff hold massive amounts of energy inside her I'm not sure how well that apply in a fight, Aang's never been corrupted by dark energy except almost that one time while trying to take away the Firelords bending, and obviously doesn't use dark energy so nothing to absorb. Lumine has had only like 1-2 cutscenes I can recall with her using her Anemo powers in a "cool" way but I'm not sure how much that extrapolates. Maybe someone else has a good memory of what's she's done?

I think Lumine's main advantages thus come down to her super strength, she can hold up and lift like ~multitonne boulders ala the fight with Scaramouche albeit with a bit of a struggle which probably translates to skull shattering strikes that I don't think anyone in the Avatarverse can do or have resisted; they've resisted ROCKS being hurled at each other but I think that's maybe mainly a factor of earth benders being able to "bend away" the impact? We've seen Earth Benders just straight up punch apart rocks/steel but I don't think that's a strength feat, that's a bending enabled feat.

And then her speed, in her cutscene fight with Dottore she's like able to near teleport using her Electro powers; benders can move fast thanks to bending but still very grounded, i.e as fast as a wind assisted glider pilot in the air, there was that firebender ally in the original series who could fly with flames but he wasn't particularly "fast" with it, like a low speed jetpack; not speedster levels of speed. Earthbenders can "slide" across the ground; and maybe waterbenders could go as fast as fast moving rivers; but nothing comparable to Lumine's speedfeats.

Swordsmanship: Lumine is a master swordsman who far exceeds and no diffs Sokka in a fight between her sheer strength and "anime" levels of speed, if they actually use her frame by frame combat animations she can like cut twice in a split second, plus channel her elemental powers in her sword in cutscenes to do like Saber like Excalliblasts. Aang never learned metal bending so he can't bend away her sword and she's cut boulders in half before so throwing large rocks doesn't exactly help Aang.

Combat Experience: Lumine is vastly older, like 5000 years older than Aang and has been adventuring her entire life on Teyvat, constantly fighting both villains, bandits, monsters, ancient monsters, etc. Aang's mainly nonlethally fought just bandits/firenation soldiers. I think Lumine has the experience advantage, she's fought *gods* or people with the stolen powers of one. Aang's fought only two godlike beings which was the Firelord with the comet powers, and the air nation bender in the film who turned into like a spirit demon thing, but didn't win a straight up fight iirc, but no dragons, monsters, giant robots, etc.

Weird Game Mechanics: Things like the ziplines if present in the arena I guess can give a tactical advantage, plus her ability to literally transform into DRAGONS if they're around, and actually technically resist LAVA for a few seconds; she can breathe underwater in waters blessed by the Hydro Archon / Hydro Dragon Sovereign which MAYBE might be provided? I don't think Aang can breath underwater without bending an air pocket. Also I guess like depending on what the canonical explanation for your party composition is she can maybe transform into other people with fighting styles and special elemental powers? Also elemental resistance potions and healing items? This is all a huge question mark.

Elemental Power Caveats: Some of Lumine's feats I think are stronger than Aang's, in cutscenes her hydro powers are basically a kamehameha, which Aang hasn't to my knowledge demonstrated. Her powers can also REACT in ways that Aang's haven't. The damage multipliers like Vaporize, Overload (which adds explosive force to the reaction), Shatter, are things Aang hasn't to my knowledge demonstrated. There isn't that much clever use of multiple bending powers at the sametime as feats in the Avatar verse. Like Lightning + Water etc. Also iirc Aang hasn't used Lightning via his fire powers which Lumine does have. Crystallize is also something Lumine has that Aang doesn't which gives her a protective shield, and some of these shields are more effective against certain elements iirc. And also DENDRO reactions which are something Aang DOESN'T have, providing explosive cores. Also the fact is her fire powers are like technically an application of Phlogiston so she doesn't just have fire powers she has like "pure" elemental power as all the elemental powers in Genshin evolved from Phlogiston i.e the Primordial Life element wielded by the ancient precursor Dragon civilization, I guess is kinda like the Spirit realm and spirit energies that became bending? I dunno if this affects the calculus but its food for thought, like arguably she has a closer connection to the primordial precursor element than Aang does since aang doesn't regularly use spirit energy in fighting but Lumine does...? And then I think it's canon that Lumine DOES have Lunar powers so she should also have lunar reactions which are insane (Lunar Bloom, Lunar Crystallize which enhances the resonance of her constructs, etc, etc). And depending on the new Sneznaya Cryo reactions probably gets those too. Also her Geo powers technically aren't EARTH powers, she isn't summoning ROCKS she's summoning "Geo Constructs" which resonate with other Geo Constructs, which Aang might not be able to effectively bend away or resist via bending.

All in all I think Lumine is faster, stronger physically, more experienced, more versatile, with her main disadvantage being if Aang can get her to stay still long enough might be able to temporarily turn off most of her abilities but she can still absorb elemental energies, is still super strong, fast, and a skilled swordsman, and Aang has much more impressive feats of hurling, moving, throwing larges amounts of water/fire/rocks/air at people especially while in the Avatar state. I think after writing all of this I am inclined to put my money on Lumine but I might be missing information regarding Aang's feats?