zoro's ambition is only relevant to him.. if he were an actual lad in this world he won't give 2 shits to what we say about it.. whether admire it or not.. plus the only depth Bullet got from the movie is him joining roger.. and being a nearly invincible human.. but zoro on the other hand was shown to start from the scratch to become the strongest swordsman.. he wasn't as gifted as bullet was he had to start from ground up.. after he got beaten by Mihawk.. and had to push himself to the brink of death to surpass what he was moments ago in almost every fight .. that is what gives him depth in addition to his pride as a swordsman ... and he doesn't need a past.. he already has a legacy forging ahead.. the only past zoro had was that of ego which crumbled once he faced Mihawk... he had to learn it the hard wayy..
Many swordsmen may yearn to become the strongest
but only a scant few would choose their burdens over their lives and not everyone gets the privilege of being told that they're just a big frog in a small pond by the same Apex that they swore to achieve... and yet not everyone gets admired for their will by the same Apex that humiliated them for being naive.
"to push and keep pushing, that is the way of the sword"
- Roronoa Zoro