He was going to lose to Buggy, and couldn't beat him. That's the end of it.
The fact that you said ''Zoro carried Luffy'' was just funny, as if Zoro wouldn't be in that condition if Apoo used 2 attacks on Zoro instead he used on Luffy, and one of them was the one that he used on Kizaru.
Zoro doesn't care about his wounds while fighting and he doesn't care about resting, so he would definitely use a technique similar to G2 if he could, so irrelevant excuses. The only difference Luffy can use a technique like that, Zoro can't. It doesn't mean Zoro wouldn't, he definitely would.
Zoro can damage Kaido, by using the scar that Oden created and the scar that scabbards damaged a little. Zoro knows his role, he will try to find a cheap-shot, while others are distracting Kaido. Luffy will still show the level difference between himself and Zoro.
Kaido is a special case because they need a swordsman to open up the wound that swordsman Oden caused before and the scabbards already damaged that scar a little, that's also why Oda used scabbards to fight with Kaido, otherwise he wouldn't do it, he also gave Oden's sword to Zoro for that reason. These are special circumstances that wouldn't happen with Luffy's other opponents, and again Luffy will still show the power difference between himself and Zoro despite Zoro opening the old wound that Oden caused and the scabbards aimed and also caused a little damage before Zoro finally opening up again. Kaido already ready for that after seeing Oden's images on his head, once he sees Oden's sword on Zoro's hands, he is already mentally not good when it comes to Oden, and he will again see Oden's images in his head when he sees Enma. So this is a special case.
You can't complain about Luffy had people saving him, when Zoro couldn't get into Grand Line and he couldn't get stronger without Luffy's crew. Zoro got stronger only because of being in Luffy's crew. He would be a low tier swordsman in East Blue, if not for Luffy taking him into his crew.