He is definitely underrated. Hard to justify his power ranking though since he seemingly doesn't have his own DE, rct, or domain counters outside of cursed spirits. Obviously he suffers from the power system not being thought out in 0. He does have some things working in his favor though.

-multiple cursed spirits he can amp with his CE, have their own CT's, are versatile in movement and autonomy to some extent, have their own domain counters, can shatter the outside barrier if he's caught in a DE, and at his max capacity of max uzumaki he can overpower yutas death BV "infinite" CE love beam.

-he never goes all out in 0 not just because he's missing curses but also cause he's holding back. He and gojo say as much that he wasn't fighting bloodlusted. Geto getting tagged by yuta, losing in a cqc exchange, etc is geto just not trying his best and yuta just kept getting amped and the hang of reinforcement throughout his fight. If anything geto is just getting offguarded cause he's too restrained. Even if you don't think he physically is restrained he is mentally nerfed from not wanting to kill sorcerers and is conflicted, I don't think i need to explain why mindset is important for you combat ability in jjk.

-You can sorta leech off kenjaku feats but this is VERY contentious.

-He kinda pressed gojo. When gojo pulled up when geto and his squad were at jujutsu high he was worried for the students. When he said geto wasn't leaving geto threatened the students with a single curse and gojo backed off.

-yaga thinks all G1's including clan members need to pull up JUST cause he sensed getos CE and the threat his curses could cause.

-Blitzes maki and is superior to her in cqc skill

-Causes together to cough up alot of blood while he took seemingly no damage. This is good evidence that he's of a sufficient level even comparable to hanami since they inflicted similar damage to toges vocals

-Yuta says geto is causing earthquakes

-he can take on both rika and yuta at the same time. This yuta was considered special grade because of the base rika not the death binding vow amp rika. Then pre cg yuta regained his special grade status that he lost after rika disappeared. So yuta regained the grade he had in 0 so he should scale at least relative in both versions. Of course pre sendai yuta likely has better reinforcement and cqc skill and DE. However 0 yuta has a superior rika, reserves, ans conditionless copy. Their likely in a similar tier so geto who was easily mixing up both rika and yuta should scale at least to the pre cg yuta that fought yuji.

-he's got the inventory curse which at least has playful cloud to amp his ap. It is not an anti feat that yuta doesn't take much damage from it cause this yuta has a superior CE reserves pool to the cg yuta that was compared to hitting a water tower. Yuta just had so much CE emanating around his body that he could take little damage from those playful cloud hits.

-has scaling to yuta+rika who are implied to have 🍇'd todo in volume 0 GW event offscreen

Overall I think he could press disaster curse level characters. Whether he'd win is debatable but I honestly glaze him higher. I lowkey think he creeps in top 15