That´s true tbh. He´s no different than sasuke, vegeta or killua.
Crazy part is the people you named are far more developed than zoro.
Episode one killua and vegeta are completely different half way through their respective series. Both having gone through multiple personal moments that shape them.
*Vegeta losing to the man responsible for killing his entire race, and feeling so helpless that he begs goku (someone he looks down on) to defeat him. Even takes pride in goku. Then he learns to call earth home and even starts a family and intends to protect the earth. Then has a father son emotional moment followed by him acknowledging that goku is better than him. Then he sacrifices himself for the earth.
*killua killed without hesitation any time he was annoyed. Managed to make a friend and tried to turn his life around, only for his family to tear him away from that dream. He managed to break free and he firmly followed a no killing rule which he only broke when fighting against the ants. He went against the deeply ingrained teaching/hypnosis of his family and was willing to stand and fight to the death for his friends. And finally cut ties with his family at the end of the election arc.
Oda gave zoro 2 dope moments. "Nothing happened" showed that zoro was willing to go back on his word to "kill luffy if he got in the way of his dream" and him bowing to mihawk showed much of the same. That was 12 years ago.