Luffy is definitely stronger than Zoro
We will see about that...
There are a lot of other factors to consider besides lethality to measure overall strength.
Sure, let's see the stats comparison.
Lethality - King(swordsman)
Physical power - King(Zoan)
Endurance - King(Zoan)
Durability - King(fights with a weapon non-stop)
Speed - unknown but considering Zoan boosting physical stats it's logically King again
DC - King undoubtedly since Katakuri's DC feats were rather poor
CoA - unknown but King is far better guess than Katakuri
CoO - Katakuri
CoC - useless but Katakuri, for now
AoE capabilities - yet to be seen, Katakuri has awakening in his favor while King could have sword AOE techniques or fire-spreading
As you can see, aside from CoO, all other stats are most likely in King's favor. Katakuri suffers because he was paired against Luffy, I am sure he would be better if he was paired against someone else who doesnt need plot armor like Luffy did but it is what it is...