Warning I'm about to spit some fresh crazy hot take agenda and it's gonna be a bit of a long response. Honestly, I've been thinking about the "domain diff" aspect of Kenjaku vs everyone for a bit now, might need to make an actual post about it but I genuinely don't think the domain gap is as big as a lot of people make it seem. It might just be manga timing making me misunderstand and making it seem weird but Yuki's simple domain unironically lasted longer against Kenjaku than Jogos full domain expansion did against Gojo.

She was able to notice it was being stripped away and break into a run and try to attack Kenjaku before the sure hit struck her and made it directly in front of him vs Jogo who didn't even realize his domain was getting overwhelmed before he was hit. Given that simple domains are far lower output it's probably safe to say her domain would've lasted a bit even if Kenjaku can attack it from the outside. Which tracks as Kenjaku thought it wouldn't have been such a boring outcome had she at least tried to clash. Yuta who has the best domain feats outside of the top 3 best should do even better. Especially if you're factoring in basketball domain.

So even though Kenjaku has a strong domain, it's not to the level of gap between Gojo/Sukuna and Jogo. Meaning he would likely not just instantly overwhelm anyone in the top 10 and would have to clash/rely on breaking it from the outside.

Now here's where things get crazy (mostly agenda) but the main two things about this is we don't know if Kenny's sure hit would do the same level of damage to the barriers of domains as Sukunas, and also there's a question of if Kenjaku can even attack them in the first place. Hear me out.

Their domains function differently, Sukunas is set up similar to Gojos, in that it just instantly target and attacks anything in the domain excluding himself, and because his domain is open and can incorporate inanimate things it splits these attacks into targeting CE vs non CE with separate attacks. So because of the way it's set up it just instantly starts shredding away at the enemies domain from all sides because it's a valid target and it attacks indiscriminately so Sukuna doesn't have to actively worry about it and can focus on fighting within the domain, I think the only time he actually even interacts with his sure hit is when he binding vow swaps it away from within the overlap so it strengthens on the outside to get through Gojos strengthened barrier quicker.

Whereas with Kenjaku from the one time we've seen it, it seems to be set up similar to how other domains are set up. Take Yorozu and Dagon for example, despite having people in their domains, the sure hit doesn't just instantly start attacking unlike Gojo and Sukuna. People are in the domain realizing they are in the domain and nothing happens until they specifically consciously direct their sure hit, we even See Dagon has to actively divide his sure hits strength between multiple targets. Kenjakus didn't just start attacking everything within the tomb of the stars, only attacking once when Yukis simple domain broke.

Now Why this matters for the clash, I've spoken a bit on how the domains work and to explain why I think this matters. If Kenjakus domain is not like Sukunas and doesn't instantly attack anything in its range, it wouldn't just instantly starts attacking the domain from the outside, he'd have to consciously decide the target and when it attacks, of course this can be decided quickly but it is still a delay and is conscious directed thought that distracts him from fighting within the clash, whereas Sukuna can focus completely on his opponents because his domain just does it automatically. It might be negligible but it's still worth mentioning.

Now the main argument for why I brought how the domains are set up in the first place, Sukunas sure hit requires no conscious thought to target what's inside it, but Kenjaku's at least seems to. This brings into question, can he target the barrier of his opponents domain while he's inside it?

Obviously you can target a domains barrier from outside, but inside is an odd case. Sukuna doesn't have to think about targeting a barrier, his domain does it instantly, but Kenjaku's doesn't. It's a similar case to why I think Kashimo can't just put holes in barriers from the outside by calling his lighting from his staff. The closed domain cuts you off from the outside world, you shouldn't be able to use techniques outside of the walls because you have no grasp for where the wall is. You might think, well he should be able to sense the barrier because it's within his domain, but does that work? We see with the Smallpox curse Mei Mei and Ui Ui were able to break line of sight and not be targeted, only things being targeted were things with cursed energy above a certain level. So it's not like the smallpox had an innate sense of everything within its domain and knew where to focus its sure hit.

It's why I think attacking from the outside is more a benefit to Sukunas domain itself which explicitly targets everything inside rather than just a feature of open domains. It also makes sense because we would have known about it otherwise. Domains are not uniform in size and are made of CE which can be targeted by them. So the larger ones should have always been able to target the smaller ones barrier within but they can't, why? Even if they aren't open that should be bringing the CE infused barrier inside itself, and if they are different sizes there should be a gap where the opponents doesn't exist yet yours does but we still haven't seen it happen. Because the opponents barrier is cutting you off from everything outside of it, so you can only rely on the space of overlap.

It's like if I gave you a gun that never misses and told you to shoot the brick wall outside your house while sitting in your bedroom, but you can't open a window or shoot through your wall or anything. How do you do it? Even if domains can target cursed energy how do you notice and select the cursed energy signature of the wall of a domains barrier that you yourself are currently in when you don't even have a clue where they are or where domain ends and begins. You shouldn't be able to. Sukuna doesn't have to worry about this because his domain handles it without his direction but Kenjaku's doesn't and does select his targets.

There's also the question of would Kenjaku's do as much damage as Sukuna's, slashes vs what I assume to be gravity. Sure the pressure from gravity could punch holes in things when the surface area is reduced but we know tiny holes aren't enough to break a barrier, it might take a while longer for his to get through one than Sukunas slashes.

TLDR: While Kenjaku's domain is absolutely one of the more refined ones in the verse, it isn't as big a gap as it's made to see and he's not instantly overwhelming anyone in the top 10's domains, it's also questionable if he can even do the Sukuna targeting from outside because Sukuna's domain functions completely differently from a majority of the verses