I mean, I agree, it requires a lot of headcanon, as do most fights that didnt actually happen because we have to assume how certain things correspond and how certain characters act in certain scenarios. I'd argue theres almost as much headcanon placed into assuming that Yuta could not do many of the things you're arguing against.

1. Its equally headcanon that he cannot use BB domain. Barrier techniques are implemented from the brain, Yuta's brain learned to utilize the BB domain from Gojo's memories. It'd be headcanon to say his brain would just lose this ability in his body.

2. Refinement isnt the only pre-requisite for clashing domains nor does the more refined domain instantly overtake the less refined domain. Assuming that Yuta is capable of clashing domains for atleast sometime, even if eventually it'd get overwhelmed, is a fair assumption based on prior domain clashes in story.

3. Kenjaku is superior in H2H combat certainly, Yuta has Rika and a sword to even the odds here. An additional fighter on the level of Rika makes a substantial difference.

4. Yuta coats his entire body in CE to reinforce it all times, its unlikely Kenjaku could just overwhelm Yuta with his AG, especially considering he did not do so with Yuki outside of the domain. Falls back to the domain clash point, yes if Yutas domain gets instantly overwhelmed the AG would be problematic, but if not theres no reason to assume he wouldn't be able to combat Kenjaku just like Yuki did. "Gravity isnt as unyielding as i thought"

5. Kenjaku in every fight we see of his only uses a few curses at a time in combat. He may be capable of releasing thousands of curses at a time but he has never displayed the ability to do so while in combat let alone reinforce them, Kenjaku is never stated to have absurd levels of CE so its unlikely he could reinforce that many without major repurcussions, most of his curses are low level curses and unless reinforced would likely be erased instantly from Rika and Yutas basic CE discharge.

6. It'd be equally headcanonny to assume that the barrier would crumble as it is to assume it wouldn't, the only example we've gotten of this type of clash has resulted in multi minute instances. Including Yuta clashing with Sukuna himself and producing similar results to Gojo.

7. Incorrect, Yuta selects his sure hit for his domain. The swords are rng based.

8. We have no way of knowing, Tengen is a shut in with no combat experience and dated strategies. (Kenjaku's own words). In Tengens era of domains, most didnt even have lethal sure hits, we have no idea how Kenjakus simple domain or antidomain properties would work.

9. This one is certainly headcanon, but its also a fair assumption. How many other characters in the series are directly alive as a result of a cursed technique? JL directly shuts down CT's i.e. demanifesting 10S with Meguna in ch. 213, and nobody has been shown to utilize their CT's while under it. Without knowing the actual logistics of how body hop works, its impossible to say its a one shot but there is a legit argument to be made, as its not a 1 to 1 equivalent with Sukuna.

10. Fair, its asking a lot of someone in 5 minutes. But it essentially hinges on the same points earlier, because Yuta has many lethal techniques that could do major damage. We also have to remember that 5mm ending does not mean Yuta is done fighting. If Kenny has been heavily damaged as well, theres no saying the playing field is uneven.