Exactly; Zoro's body condition is the most human-like in the monster trio, which is why he's the underdog who always has to struggle the most to be somehow comparable to the other two. He's also the only one who needs weapons to fight, while Luffy and Sanji just use their bodies (leaving aside Sanji's raid suit, which he already destroyed anyway).
My point is precisely that Zoro has never been monstrously strong like Luffy and Sanji in terms of durability and endurance, which was already made quite evident by what happened in Arlong Park, when Sanji had also been seriously injured in the previous arc (5 or 6 ribs broken by Pearl + the damage from 10 hits of Gin's steel balls, which were much more powerful than Pearl's shields) but Zoro was the only one whose injuries were a relevant problem in his fight.
In Enies Lobby too, Sanji was terribly hurt by Kalifa, but was still able to beat Jabura faster than Zoro beat Kaku.
And in Thriller Bark Sanji had a sword pierced through his body while protecting Nami from Absalom, but he could still fight Oars as if nothing had happened, without seeming to feel any pain from the injury, whereas Zoro stayed in coma for days and still felt the damage in his body when they were already in Sabaody just because he took Luffy's damage in Thriller Bark, which was basically just the damage from some bats and the recoil damage for using Gear 2 and 3.
What happened in Onigashima is just another example of it: Zoro is the only one who needed a special medicine in order to heal the bones of his body so that he could be in a condition to fight, and that because of an attack that just hit his swords that he used to block, and not even his body directly, whereas Luffy took a lot more hits from Kaidou directly on his body, and is still laughing, without any medicine, and Sanji too, who had already began his fight with Queen after being a lot weakened and almost killed by Black Maria, after being crushed by Queen he was able to recover all the bones of his body to normal on his own, without any external help, and then managed to send Queen flying to the sky, just needing to sleep for a bit of time afterwards before waking up and being active again as he is now.
And sure, you can argue that it's more meritorious for Zoro to be strong without any magical or artificial modification in his body like is the case of Luffy and Sanji (though only since this arc, because before he was also naturally strong), but so what? This doesn't change the fact that Zoro is not as strong as Sanji and Luffy, nor the fact that Zoro needs some very powerful magical swords to fight, whereas Sanji and Luffy just rely on the strength of their bodies as they are, which may not be a natural strength, but is still the strength of their bodies themselves.
