Remember Ulti clashed equally with Luffy's CoA who's probably stronger than Katakuri in terms of CoA now.
You're confusing a few things.
(1) Hardness of your attack is not just dependent on your CoA. It's also dependent on the hardness of your body/DF. Jozu's attacks sting not just because of his Haki, but also because he's made of diamond.
There is a reason he coats his arm in diamond.
It's not just about Haki. Haki + Diamond = More durability.
It's the same thing for Ulti. A pachycephhlosaurus has a tough/durable head made to headbutt. So we can't ascertain Ulti's level of CoA, because her head is already super tough to begin with.
(2) Like I explained in the other thread, there are different types of Haki. Katakuri still has better Color of Armaments: Hardening, or Busoshoku: Koka than Luffy.
As Oda wrote, "Busoshoku" is the category of Haki, "Koka" (hardening) is the specific model. But Luffy is training in penetration Haki, which is a completely different branch.
For example, you can't say Katakuri has better CoO than Enel, because while Katakuri can see more forward into
time, Enel can hear a pin drop on the side of the island, so he can hear further in
space. Again, there are different types of Haki, even Rayleigh mentioned this.