I thought full power Zeus was too powerful for Nami, it didnt make much sense.
Now, even if Zeus was able to escape in the climat tact he got a decent chunk of the soul taken away (rest was supposed to get eaten by Hera) meaning he's decently weakened/nerfed, giving Nami a power-up without making things unbalanced. Mom doesn't get nerfed either since she now got a more competent homie and took a portion of her soul back too.
It also solves another problem : there's a valid reason for Zeus to now be with the straw hats instead being loyal to Mama; she'll kill him on sight, Also if Hera got tricked into believing the power surge she felt was Zeus instead of the weather balls, it's the type of trickery that fit Nami's character.
There will always be complaints but Oda did a pretty decent job making it work imo.