How strong is mc gonna be able to get? (Goated explanation btw thanks) btw who are considered natural superhumans?
MC probably lands around Arbiter tier at the highest by the end. Lowest being Natural Level 5.
As for the Natural Level 5 Superhumans. It's superhumans who evolved naturally while completing their requirements to evolve. Doing it rewards them with gifts in the form of unique abilities or mutations of their powers. It also likely grants a greater amount of internal power and increased power growth as well.
This is a pretty good list all things considered, although I'd put the natural level 5s above the chosen. I don't think there's anything to imply that Eiseth was particularly weak among them, it's just that Bernhardt is way too strong.
There's also the question of whether or not every natural level 5 would be as strong as that trio. They could simply be exceptions within level 5s regardless of being natty, or maybe having potential as crazy as theirs is a requirement to becoming a natural level 5 in the first place. So accordingly, if all natty level 5s are that strong that placement is too low, and if the trio are just exceptions then there shouldn't be a difference between them and artificial level 5s.
In any case, I don't see a world where the chosen and natural level 5s are of relative power.
Eisheth couldn't hold back Malik without the help of her daughters, Strength Eaters and Undines during the Battle of Diamonds. She didn't try to fight him afterwards as well. Leaving as soon as he broke out of the prison. Syla was able to use Eisheth true form to attack Indra and it did nothing to him. Then lastly, a suppressed Bernhardt defeated her with ease in her true form.
With that level of showing, it's clear that Eisheth isn't ranked that high among the Chosen. Especially when Ella believed that Aglaecwif could outright end Nyx and Malik during the Battle of Diamonds. So Eisheth would be comparable to the expert Level 5 Superhumans aka the Captains. In her fight with Nico, she needed assistance from Hex or she would've been in the sun. That wouldn't have killed her, but she would've lost. Then it's her comparison to Lexi in and outside of the dream.
Eisheth however dominated Kira and Elijah with no problem. By a large amount at that too. Especially since she didn't use her true form at all for them. So Eisheth would be around the Captains tier. Most "Artificial" Level 5s likely won't be able to beat her without having comparable power or an ability suited to beat her.
As for all of the Chosen not being on par with the Natural Level 5s. That remains to be seen and depends on the Chosen in question. Chosen have the Apostle traits. 2 of the 3 known Nat 5s have lesser traits. Indra, by virtue of being an Apostle Avatar and Chosen, would have to be on par with them. Unless you believe Level 5 Superhumans can beat Apostles. There's also the fact that Valravn, even while weakened, could nullify Nico's powers. Reminder that Valravn dropped from S+ to C+ levels of power and still could stop her power. Aglaecwif has her mysterious language of the void magic or whatever it's called. That's on top of her connection to the Immaterial world.
So, for me, Chosen are above Level 5 Superhumans who haven't had their powers as long and used a serum instead of reaching completion. Which essentially points to majority of the known Level 5s. There's a few exceptions, of course. But I don't see every serum taking Superhuman being capable of beating the Chosen. The reverse is some what true as well. Hence, Chosen are above Level 5 (should've specified that I meant Artificial) and around the same ballpark as Nat 5s.
So with that in mind. They would fall within the Natural Level 5 Superhumans tier, for me. Especially since some Chosen themselves could be Natural Level 5 Superhumans, who failed their 5th Evolution and/or flat out turned into monsters. Syla potentially being an example of this. Hell, for all we know, Indra is actually a Natural Level 5 Althuman. Which is why he was rewarded with being an Avatar of the 2nd.
For the Ella mention about Aglaecwif about being able to end the Captains. It's in her letter.