Bounties are given from what the WG saw, were told and many other things.
So Killer defeated Hawkins, help Kidd but didnt really did a thing.
Example, if Usopp was on the rooftop, he also would had hitted Kaido once if he was hiding in some rocks and targeting him, his participation won't give him a billion bounty, but his real achievements. Example Raizo vs kaido, could stop his fire and return it, and? That doesn't show enough, his power level is still not settle.
So Killer given some hits won't show his power when letting your guard down vs multiple fighters always happens.
Killer at best will just get an increase for defeating Hawkins.
That is the reason Chopper didn't get a huge bounty, his biggest feat was not fighting Queen, but doing his potion things.