You're right! It's too soon to decide anything. I've yet to assign a fixed level for King actually. But we can still compare what we know about King with that of his fellow commanders, can't we? And whether or not I am juping the gun, I am at least not assigning him fixated predetermined level regardless of how good his feats are, and pretending that everything he or his opponent does falls beneath that preset level. I think my approach is more reasonable than what most others are doing to say the least.
I agree the commanders aren't perfectly well rounded—that's why they aren't top-tiers. Top-tiers come with a complete package; being an all-rounder is what seperates your average top-tier from one-trick ponies like Marco and Kuri. While King isn't nearly as good as the actual top-tiers, he's certainly looking decently better than his peers in that regard— and that is on top of being nearly as special as them. I've already said that my intention isn't to say Marco and Kuri are weak without their special traits but they pale in comparsion to King.
I also agree there are areas where people like Marco shine so much that King can't even be compete. But I'd say you can be much more competent as a fighter by excelling in multiple areas that matter. I don't think the length of a fight doesn't determine a fighters competence. Dressrossa Pica, for example, would take twice as long to be beaten by Zoro as Vergo, but Vergo would pressure him much more. I am not necessarily trying to say struggling to hit/hurt your opponent doesn't count as difficulty; but I am sure you understand what I am trying to imply by saying, "Vergo pressures him more Pica."
Also, if Zoro ends up one-shotting King; it just means Zoro is that overpowered. It doesn't say anything about how King compares to Marco and others; the same way base Kaido one-shoting Luffy doesn't prove Kuri Luffy is weaker than Katakuri, who wouldn't have let himself get hit. Zoro may not be able to beat Marco or Katakuri as quickly as King but that warrant a fight of higher difficulty from them, unless you wanna equate the length of the fight with the difficulty level.