dynamics are a tad different I think
not sure gaban is as relevant as sanji so I could see his bounty in the 1 bil mark and not be surprised.
Roger had a vice captain or partner
straw hats have none formally but luffy has" two wings" , while zoro is stronger than sanji
one has not been explicitly given more importance in the crew than the other.
its a massive difference.
so I reckon Rayleigh would have a bigger bounty Gap on Gaban than zoro has on sanji
and Roger would have a similar bounty gap on ray to what luffy has on zoro.