Hmm. It's only to be expected that Kaido will recognise Enma given that it's one of only two weapons that gave him his most grievous scar.
It is currently Zoro's most powerful sword.
Besides, if I'm not mistaken, doesn't Zoro have his haki overflowing from the blade:
This resembles the overflowing haki we saw from Roger and Primebeard during their clash.
This seems like a standard very powerful attack reinforced with COA haki to me.
The Scabbards did not literally have Oden's Ryuo though. They just had ryuo sufficient to harm Kaido.
I don't really buy this in particular. It's not like ryuo lets you ignore Kaido's durability (at least not in the case of Oden/the Scabbards), it just let's you deal more damage. Kaido is not a logia or something similar.
Ryuo boosts your AP, and it boosted the Scabbards AP to the point they could damage Kaido.
I don't really believe this TBH. I think the Scabbards Paradise Totsuka would have done more damage to almost any character than Supernova attacks.
The Scabbards can be above Supernova in the narrow realm of attack potency. Don Sai was greatly above Pre Raid Suit Sanji in that domain despite being weaker than him. Elizabello as well.
With Enma and overflowing hardening, Zoro is simply capable of displaying top tier attack potency.