Becoming loyal to Luffy is something every Strawhat did. None of them is more loyal to Luffy than the other. Every Strawhat is willing to die and sacrifice their dream for Luffy.I see.
Zoro just had a different situation. One similar part of his development can be described as he initially even threatened Luffy and later on went to become pretty much the most loyal of the crew, to the point where he would force luffy to stay on the right path and put luffy's dream, specifically, before his own life long dream of becoming the WSS. And this is important because of how he was in the beginning. Obviously different events lead up to it.
And that's just one part of the characterization and it's development in the series. Zoro obviously doesn't have much backing him up when it comes to characterization from a backstory, even his own dream wasn't explored much but he good development regarding his ambition and relation with Luffy during his first confrontation with Mihawk within their travels. So I do think that what he get throughout the series do make up for it.
Ambition isn't enough IMO. Everyone has ambition.