I still don't think King has higher durability than Kaidou for two reasons.
1) Kaidou didn't block Zoro attack while King blocked with his wings.
2) Zoro sword didn't touch directly while his sword touched Kaidou scales directly when he used dragon twister in the rooftop.
Either way, King is looking good. This fight is looking good.
Also, King is superior to Katakuri in durability, attack power, probably endurance. Rest of the stats are in Katakuri favor.