Dying for your friends is different than dying for their ambition.
Protecting the crew at thriller barl fits perfectly with zoro's swordsmenship, "to protect what one wants to protect" zoro succeded in that. It was his swordsmanship that saved his crew.
Nothing post TS proves that zoro places luffy's ambition above his own, yes he trust luffy to achieve his dream but luffy too trusts zoro to do the same they were working together to achieve their dreams.
Also putting your life and ambition on the line to save a friend doesn't mean you place their ambition above yours, otherwise luffy considers robin and sanji's ambition more important than becoming the PK since he too sacrificed his life for them once.
Zoro swalowed his pride to ask mihawk to train him following luffy's decesion of taking a break and getting stronger for the new world, luffy too swallowed his pride and bowed two times to save his freinds the 1st at drum kingdom looking for a doctor for nami and the 2nd at amazon lily.
Life and ambition worth nothing when it comrs to saving a friend's life, that's why whitebeard pirates sacrificed hundreds of comrades just to save ace, it was never because of hierarchy, but rather friendship.