Zoro with broken bones shouldn't even be moving. So how exactly is he being limited especially after discovering a new technique on top of using his strongest attack? He's pushing himself past his limit and doing attacks he normally wouldn't be able to do.
Your strongest attack at 10% is still your strongest attack at 10%. Doesn't matter how you look at it he was in a weaken and poor condition.
You have to look at how much of his new power was put into his attack. The attack wasn't new, he learned that sometime during his training probably during the time skip, it was just the adv CoC he used. If he only put a small percentage of adv coc into that attack then that attack could still be much weaker than that same attack without adv CoC but in much better condition. Do you believe a character's strongest attack at 10% is stronger than their second strongest attack at 70%?
You must understand, characters doesn't have to be severely injured and in a poor condition to be pushed beyond their limits and gain new powers. Look at Zoro's battle against Kaku. He wasn't 100% but he wasn't severely injured or in a weaken and poor condition. Yet, he still gained a new power.