Akainu was scared of kinemon lil bro
But Kizaru apparently isn't and yet he's Akainu's subordinate. That's the ever so long history of Admiral haters. They can't provide arguments that make sense. Akainu is still > Kizaru. Only thing that changed for him. He has the burden to lead a military force whereas Zoro's captain gave the OK yet he chickened out.
and yet both zoro and akainu are showing the same attitude here who they're holding back is irrelevant
It isn't. Akainu is leading a military organisation, has to think about the future and has to explain himself by superiors if things don't go their way. Zoro's captain gave the ok yet Zoro didn't want to become he doesn't want to pick a fight with the Navy.
When Akainu stopped Kizaru there was never any word of the Yonkou being the reason.
A small but important difference.