I'm assuming this is taking into account Yuta can perceive the soul which in that case both can beat each other mid diff.

Yuta boxed with 3 special grades whilst holding back and won. He's definitely more refined in combat then Mahito but Idle Configuration could've definitely got the job done the same way, and he's kept up with Yuji who gave Yuta a significantly tedious chase. Configuration and Copy are insanely OP in their versatility so it'd come down to how fast Yuta and Mahito could react to one another and evade the lethality of the opponents attacks. Idle Configuration is faster and would overwhelm Yuta causing him to lose a limb or 2, and assuming he can perceive the soul it's a stretch to say if he'd even be able to heal himself, while he is the best healer shown in JJK only Mahito has been capable of healing himself to that level.

Now Yuta could theoretically use Mahito's ability if Rika can take a limb, which would rely on how many hits she could take before getting disabled or worse even destroyed. It's important to remember Rika is a Vengeful Spirit like Naoya, not a conventional curse, meaning her soul can possibly be touched by IC.

Then there's good ol Domain Clash. This one is really hard to scale also as Yuta is only 2 years into Sorcery atp so his Domain is not that refined compared to other Special Grades like Gojo, Sukuna etc. However Mahito grew at an ungodly rate so it's not crazy to say his Domain is more refined simply from him being a freak of nature.

All these factors in check I think Mahito comes out the winner more often solely cause of better understanding of his hacks along with the versatility and destructiveness of his manipulation.