Being trained by human martial artists doesn't give her powers. It makes her an effective fighter.
MC was also trained by a human, but has still started to learn to use his powers. Are you implying that he is able to have some self-taught knowledge but Diana is not?
On that note though, Rin and her group are often referred to as martial artists, but use magic constantly as part of that. So "martial arts" doesn't imply only mundane, physical training.
MC is trained by Eliza's Father. So he is also an effective fighter, although maybe not to her level.
Regarding Oren, per dev:
What we learned from Oren is far from the best available in the world, he was skilled sure and he taught us what "he" knew
Oren was skilled, but not at the same level of teaching as multiple of the best teachers available in the world.
Whereas he has gained some supernatural powers, one of which is the ability to absorb any that she might have.
So I'm still not seeing any way that she would easily defeat him.
Diana also has supernatural powers, and the ability to absorb powers is mainly useful for
growth, which MC has only just begun, or permanently rendering someone crippled. And he's not going to do that when he's just trying to
subdue her (as Buu explained in the quote I shared).
I'll share that relevant line again though:
1: we were not fighting on equal footing, she was fighting to kill, we fought to subdue, hence why no lazer beam / mana manipulation.
Mana manipulation is the name of the absorption power.
Is that saying that The Ancients are equal in power to Celestial gods? The "==" seems to suggest so.
If that's the case, then her potential will presumably be similar to MC's.
But MC's is untapped atm.
Has she been trained by The Ancients? If not, then her potential is also untapped.
So still not seeing anything, from the dev's words, that show her as being able to easily defeat MC.
I think you misunderstand a bit about the Ancients and those with their blood.
Each person born into one of the ancient's bloodlines, has a chance to be born with a strong affinity for that bloodline's element, but it's rare, think of it like 1 in a 1000 born to the bloodline will be born with the gene and the rest are just regular humans with no magic what so ever. Rin and Diana are both such cases. And there is one ancient per magic affinity, so fire, water, ice, arcane, wind, lightning, earth etc etc etc
So Diana is from an Ancient's bloodline, but is not one of the "official" Ancients herself. So while the Ancients themselves are roughly equal to Celestial gods, Diana herself would currently fall in the "high tier mortal being" level as well.
As for the rest, Rin is an example of someone that has learned to effectively use her Ancient bloodline, but definitely has not trained directly with any of the Ancients themselves. Aside from enhanced physical abilities, much of their power draws from their elemental and magical affinity, which can be trained by other magic users to varying degrees.
It's safe to assume that when she realized she had magical ability, she sought out the best teachers for it and they were provided to her by the nobles.
