Is it just me, or is the ending a bit unbelievable?

.

the man had his troubles, was in pain and full of hate. he knew his path was radical and probably not the solution. he questioned himself already

Instead of killing Zephyr, Luffy chooses to spare him, showing Zephyr that not all pirates are evil and that some, like Luffy, embody ideals—such as protecting friends and dreams—that Zephyr once fought for as a Marine

he aspired to be a hero in his youth and after the fight, he respected Luffy. that's why he decides to once again, protect the innocent.

the man is very troubled and well written. that's my favorite part of the movie and to me, the very best.