It can alledgedly destroy planets.
Not that you'd know that from FUCKING RISING ULTIMATE. **** that form so hard.
Here's how it breaks down.
Most Ultra Kaiju, on their own, are about Godzilla level or weaker. Hell, the original Ultraman fought what amounted to Showa Godzilla with a neck frill, and killed him rather easily. And honestly, that's about how powerful Ultraman is. Powerful enough that he just outclasses Godzilla entirely.
Gurren Lagaan is a shitty comparison because it's an anime, and they can take liberties with things that Kamen Rider and Ultraman can't. However it's not too far off for a comparison because Ultras are solar powered energy beings that can survive, and thrive, in stars and are able to throw down with the worst creatures around.
The top of the list of the most powerful Ultra villains would have to be Enpera, who was so powerful he could cover the Sun in a strange stone, and him simply *ARRIVING* on Earth made an entire city go boom.
Then we have Belial, who took on almost all of the old school Ultras and beat them hand to hand, most of them standing no chance against him.
Then we have Hyper Zetton who is *LITERALLY* a DBZ character with his insane teleportation and everything else.
But if you want to look at Ultras, you have two that stand above every single threat shown.
Ultraman King, who is basically a God that can create miracles, and defeated Belial with a literal wave of his hand, trapping him inside of a moon *THAT HE CREATED IN THAT MOMENT WITH THE SAME HAND WAVE*.
And Ultraman Noa, who *IS* a God, that punched some one so hard they went into space.
The Ultra Verse just generally out classes Sentai and Kamen Rider.