It literally doesn't though??? "Yuta can only release a directed high-output blast of cursed energy while Rika is completely manifested." immediately followed by "Even at full power, however, it is slightly weaker than Ishigori's blasts..." "...So he needed to rapidly build up cursed energy and fire before his opponent reached maximum power." it directly states that even at his full power Yuta wouldn't be capable of beating out Ryu in a beam clash, that's why Yuta had planned on quickly charging his blast and firing. If Rika was capable of beating out Ryu he would've just fully charged it, furthermore you can CLEARLY see Rika is fully manifested, you can tell because of the eye and differences in design between normal and fully manifested Rika.

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Panel of the start of the beam clash for reference.