This is about assuming battle matchups, not assuming one’s strength level. If that was the case I could make a random argument for a lot of the cast who haven’t shown a thing yet.
Again, everything we're arguing about is random since we don't know how these match ups would actually play out in the series itself.
Saying he has a main character growth rate would be to show he grows more than other side characters...Just like when he developed the dimension slash mid fight, or he learned mana zone mid fight. If Mero appears again she probably wouldn’t have grown as much as him. You said there’s nothing to say she hasn’t grown as much as him, but the reverse is true. What even implies she’s grown as much as him? Someone like Yami who consistently grows when he’s back is against the wall, while Meroleona hasn’t shown that quality.
He's developed in battle, but it's not an everyday thing. He doesn't bust out new spells every time he fights. We can only go with what we know. We can't just add "limitless growth" to his moveset because that isn't a feasable argument and it isn't fair for this tournement where we are using what they've only shown currently.
I know the reverse is true, the point is we can't make that call because she hasn't shown up and we don't know how much she, or any of the other Captains, have developed over these past few months.
You can 100% gauge a gap between them pre skip, you simply have to compare their feats. I’d argue by the end of elf arc Yami is on her level, which wasn’t the case at the start of the arc.
You could easily argue that Mero was above Yami at the start of the Elf arc, mainly due to her insane mana zone, but Yami caught up a lot by the end. She doesn’t get the benefit of the doubt about Dante, especially since he’s this arc’s strongest antagonist. Her being a royal doesn’t mean much to me, as Yami isn’t that far off and has better magic than Meroleona in general.
If we compare their feats, Mereoleona still had the best feats by the end of the arc between the two. I don't see how Yami caught up. He demonstrated Mana Zone by the end, but that doesn't mean he was on her level. Yuno did the same thing and he certainly wasn't on her level yet.
Her being a Royal should mean something as the mana it provides is a part of her arsenal. Nevermind the fact that Royals being stronger naturally is one of the main themes of the series and the key cause of discrimination in their world. I can't say anything about him having better magic as that's largely subjective. It doesn't take away the fact that her magic is strong either way.
Meroleona doesn’t have any current feats, and seeing how dominant Yami was against the arc’s strongest antagonist she doesn’t benefit of the doubt.
I mean, if that's what you think, that's fine but I think she deserves the benefit of the doubt given how strong she was. As I said, aside from Black Moon, nothing Yami did isn't anything different than what Mereo could already do.
Referring to how he was also able to fight on par with Patolli, and Lolopechka's comment about possessing the potential to defeat a devil, where she name checks both him and Julius.
Patolli, at that point in time, was not only holding back, but he himself stated his combat ability was inferior to Rhya, Vetto, and Fana. Patolli is strong,
And, as stated, those two were just examples of individuals who don't have "natural" magic who's nature appear to be inherently harmful to devils. As we saw when Yami first went up Zagred and was the only person among Charla and Licht who could harm him. In that same chapter, they were used as the lead up to introduce the concept of Arcane Stage Mages.