I think their bounties are okay when you look at it this way:
Zoro is a secretive man, wouldn't it make sense his revo army makes sure they don't show any connection to him?
So I think everyone got their bounties while being lowkey. Remember they're all split across the seas
& after the incident at the reverie, I can assure you their bounties will go up. It is possible they earned those bounties while keeping their connection to Zoro and the revolutionary army private.
Either they got those bounties by being lowkey, or after the stunt they pulled that is their bounties off rip & only Mentally ill Ace gets a raise from 602.
Considering they don't know exactly where they rank in dragons army, they probably give them sizeable numbers without overduing it because they don't even know what Zoro is plotting.
Even Mentally ill Ace was shocked to see he was found out in dressrosa.
Koala & Hack stayed hidden too so its possible even they don't have bounties yet. Remember when they just found out Rotty was a part of Father of the year's crew after Impel down?
I think they are okay. It's the fans who mistook the the RA to be a Akainu’s hype tools like force while it's clearly not.
The commanders all have bounties comparable to shichibukai and worst gen members. Those are pretty much the highest figures outside the the YCs and Akainu’s hype tools captains.
Kuma should of been definitely on that level too, too bad he might be out forever at this stage. I would like to acknowledge what happened to him at last. The situation is not quite clear if I recall correctly.
Only justified if Zoro's bounty is ridiculous. But I don't think it is the case, he probably has higher bounty than Father of the year. So it is unacceptable that not even the number 2 in command have at least a billion bounty.
Just another proofs that My drug dealer writes random numbers when it comes to bounties. Only Warlord have a nice excuse for having Virgin killer bounties.