From the trad I saw : Yuji saying he believes Yuta can do it and Yuta not denying it, is a statement to make us know that Yuta is a big deal and can likely do it. Nobody say it will be easy or else. But Yuta can likely fight 15 fingers Sukuna.
21 fingers Sukuna full power is likely => Gojo, they are comparable but Sukuna might be 1% stronger
Yuta said he was inferior to Gojo, but Yuta has Rika and a HUGE curse energy stock.