Lol in the scan he posted that was supposed to be WBH getting harmed, it looked clearlylike Hulk and Betty had powered down from the world breaking levels. Moreover even then, Hulk being sliced by a blade wielded by a person who was his equal strength wise is hardly representative of low durability especially considering the impact he endured unscathed as well as his no selling of wendigo, Armageddon and bi beast simultaneous attacks before even going full out world breaker.
The rest of the scans are not even Wbh. Additionally there is really little comparison strength wise between Kuurth and Wbh and Wbh having lower durability does not mean that he will be unable to hurt Kuurth with his vastly superior strength
The thing about strength is that there are two kinds:
Natural strength and Effective strength
Effective strength > or = Natural strength
I'll explain the difference using Superman.
Superman not only has a great natural strength (lifting or punching while grounded) but he has an even greater effective strength due to his flight powers. His flight ability can amp his punches and lifting to much higher degrees. Hell his flying strength alone has proven to be planetary.
WBH definitely has the greater natural strength than Kuurth (not debatable),
but Kuurth can use his unstoppability enchantment to reinforce his natural strength and thus making his effective strength probably comparable to WBH's strength (it's up for debate now).
Lastly, Kuurth has a different natural durability than his effective durability. When Cyttorak took his powers, and Thor once robbed him of his force field we seen Juggs still hella durable. Why? Because he was still strong. Being strong automatically amps your durability (in comics and real life). So adding a force field or cyttorak powers increases his durability and makes his effective durability even greater.
IMO, there is no way herald level beings can physically harm a FP Kuurth with both Serpent's power and Cyttorak's power. Kuurth with only Serpent's power is a different story though.