Zoro is really such a wonderful character Oda took him outta Buggy's crew and threw him into being Luffy's first nakama
In this manga Zoro's true strength and maximum potential has always been a mystery if one stops to think about it
1- yea the guys badly damaged almost everytime hes pitted against an opponent considered a worthy adversary for the arc you could say
2-Being a 3 sword kinda man i recall twice fighting while he does not have all three of his swords: against Ryuma with only two swords, but also against Hachi in AP
Johnny & Yosaku's swords were pretty big pieces of crap if u ask me though Zoro got the job done
My theory on this Zoro is that Oda is deliberately keeping him horribly damaged in many arcs for the specific purpose of him staying at #2 in the crew (obv below the captain), not only in terms of position but also in terms of fighting potential. We had a glimpse of Luffy vs Zoro in a quick few punches being thrown at Whiskey Peak, which showed us that they both seem to be on par with one another
There during the fight where Zoro decided to punch a woman and take out all the bounty hunters, Igaram or whats his face commented on that Zoro looks like the real one with the 30mil on his head instead of Luffy.
Theres was also an anime filler where they kinda duked it out, not canon for sure but still a good viewpoint on the 1st mate being pretty equal in potential to the captain.
If Luffy does not remain the top dog of the entire crew, and the number 2 is shown to be stronger or equal to number 1, that throws the story off balance and makes ppl go WTF
Another view could be that Oda has a purpose for cuttin up Zoro all the time due his swordsman status. The samaurai cliche Oda keeps retelling for the part of Zoro looks like probable cause. Establishing such a well inclined character as a guy who remains as second best doesnt seem all that appropriate for someone of Zoro's potential but for good storytelling it must be done
In conclusion, I believe that Luffy and Zoro are men who fighting wise are both equally on par with each other but Zoro must remain at a handicapped position in order to make the readers feel for the guy and establish him as second in command though he can match 1st