Since, from what I can see above, the anti star arguments are laughably bad, here's my comment on the star stuff
We know from Sellen that Radahn stopped the constellations, we know from several items that he stopped the stars, we know from other items that people know stars and meteors aren't the same so we can't even use that as an argument, especially since the only thing that could be stretched to mean it was all meteors is Blaidd's line after his death being taken above everything else in the game
The argument that Radahn stopped the Earth instead of the stars falls apart when you realize that means he's
controlling the day/night cycle and moving the stars around the planet so they show up at night anyway, not only would this also be tier 4, it's never implied and he's also uhh, insane, which makes this illogical to assume.
Another minor thing, we can actually see in Radahn's death cuscene, that the stars in the sky get brighter after he dies, even before we see the meteor streaking toward Limgrave some stars start glowing brighter again instead of being dim
Onto the Elden Beast thing, I'd assume the argument against his nebulae(?) making would be "it's in the Erdtree so it can't be full sized stars" however you should realize that the Erdtree is not physical, as things grown from its parts are explictly known as illusory
A golden seed, found at the base of an illusory tree. When the Elden Ring was shattered, these seeds flew from the Erdtree.
The Erdtree also is clearly non physical as we can see it doesn't grow into the ground, no it clips through it and is translucent, the ring (which the beast is) is noted a few times as being able to manipulate the tree like it manipulates the golden order, and the realm the Elden Beast brings us to also contains several other Erdtrees, this combined with the fact that even Radagon's room is only accessible through teleporting, not like we physically walked into the tree and just walked to the center, clearly shows that the inside of the Elden Beast's realm where it made these nebulae isn't limited by the size of the tree (since it contains more trees anyway), and so this argument can't be used to dismiss it
Then there's Ranni's ending where she says she was going to move her order (she tells us this is the night and stars) an infinite distance away from the planet, so that it was out of sight and out of mind of the people, and had no influence on them, this is another blatant tier 4 feat especially when combined with the visual of stars moving closer into the center of her dark moon, showing she did in fact, mean she's moving the stars away like she said
The ring as far back as the trailer was also noted as being able to control the stars, there's not exactly an argument that's even possible against this one, this one also backs up the Elden Beast (the physical form of the ring) making stars in its realm
So in conclusion, without a lot of unsubstantiated headcanon and ignoring lines, Radahn's thing is very clearly tier 4, the Elden Beast's thing is very clearly also tier 4 as the only argument against it is "b-but its in the tree" which is weak as I've addressed, Ranni's ending also very clearly talks about moving the stars and shows it, and then the trailer even establishes this as a power of the ring
The only feat related to stars that I can even see as able to be contested is Rennala's, if you decide you think it was all an illusion from Ranni (an illusion that calls herself Rennala, talks to you when you die, and talks to Ranni when she loses, and one that despite being so powerful, Ranni never uses on any other threat, if it wasn't clear enough, I think thats a bad argument too)
As for who this would scale to, the issue with Radahn is that he's really, really early game, like, the festival opens after getting both medallion halves or reaching Altus, and he's leveled appropriately for pre Leyndell content, it's clear what point in the game this fight is meant to have taken place during. Which means this scales to the Tarnished from early/mid game (for the sake of this I'm saying early game as pre capital, mid game as capital and Altus/Volcano Manor, late game as mountaintop, Mohgwyn, and Haligtree, and endgame as Farum Azula on)
This means it scales to the majority of demigods, something consistent with the fact that even if they were weaker, they were still relative to Radahn, given he didn't just kill everyone instantly and then fight Malenia.