Ranking power and ability-wise is hard, but I'd say Nico has the most potential out of everyone on here, but he arguably hasn't surpassed Percy (and Jason and Thalia).
If we do place Nico at number one, Percy and Jason come next at about the same level (though Percy might be a tiny bit higher because of feats). Thalia also comes close, and I've seen viable arguments for her being stronger than Jason because of her skill as a Hunter of Artemis, but the fact that she can't fly puts her lower than him.
Next we have Piper, Leo, Hazel and Frank. In my opinion Hazel>=Frank>Leo>>=Piper. Hazel and Frank are interchangeable and so are Piper and Leo to a lesser extent.
Now unfortunately Annabeth's intelligence isn't enough for her to compete with any of the seven (she could still probably take them in a fight but power and skill doesn't equal to being able to beat in a fight).
Contending with Annabeth are Reyna, Clarisse and Luke. Skill wise the list is: Luke> Annabeth>= Reyna> Clarisse. But Clarisse also has the Ares aura or whatever it's called and Reyna can boost the powers of others. So my ranking for them is Reyna, Clarisse, Annabeth and Luke (Annabeth's intelligience overcomes Luke's skill).
I exclude Magnus and Samirah because ranking them would cause quite a few problems as they have never encountered and therefore we have little way to scale them to each other (Yes Percy encountered Magnus in the third Magnus Chase book but they didn't fight or anything). If I had to estimate I would put Samirah somewhere around Hazel and Magnus just under Frank.
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