Their bounties is precisely because I don't buy the "bounty represents the danger the WG feels towards a person".
The Revo Army is, aside from the SH's, the MAIN threat they face. For other pirates, they use the Navy to fight them, but the Revo Army DIRECTLY fights against the WG.
Now, there could be reasons for that.
WG doesn't want to hype them and make them more known then they would like. Dragon's ideology spreads and it can get out of control pretty quickly. Trying to conceal their level of threat from the general public is a valid strategy.
But this is all speculation.
Oda doesn't say shit.
He doesn't bother explaining anything.
It's a question after a question after a question, and when he gives an answer, it just generates more questions.
I'm honestly giving 0 fucks about this cheap strategy of "keeping people guessing". One thing was doing it in the beginning of the story, but for something that he insists in saying we closing to the end, he doesn't feel very inclined to start answering some stuff.
I suspect that's because he intends of mixing every single piece of plot in this "final war" event. It's gonna be a shit show.
"Joy Boy"? "Sun God"? Not different things. All the same shit, etc.