They really can't read
Zoro got the bounty because of multiple things he did as SH Pirate crewmember. He even says ''Luffy's swordsman'',
And ''SH pirates'', yup, Zoro got bounty because he was recognized as
SH pirate crew member
since Whiskey Peak, while Sanji wasn't. The moment they recognized Sanji, he got even a bigger bounty than Zoro got. So that wasn't just beating Daz Bones, also Whiskey Peak and due to recognized as ''Luffy's swordsman''.
The only difference is Zoro got his bounty first, but still lesser than Sanji's. But then he fall back of Sanji again, Zoro couldn't be a Worst Gen member without Luffy's help, stop kidding yourself.