How pica is not dangerous lmao ? Not everyone in OP world are superhumans. If they are 7 billions, only maybe 100 can face him, others will be dead the moment he moves. I mean a mountain sized golem walking and destroying cities with one blow is not dangerous for humans ?
Who cares about sea ? It's not like Luffy and his crew are fighting above sea everytime, it's even rare ...
Bounty are based on the threat they are, let Pica takes control of Red Line you will see.
And Pica's stone ability isn't really that terrifying for top navy officers. Yes, its big, but Pica is also not very smart, and more arrogant than capable when it comes to fighting. Pica's statue destoryed a few city blocks with a punch. Nowhere near an entire city.
This brings me back to Zoro. They already sort of gave away how much of a threat they saw Pica to be when they gave Zoro a 320 mil bounty in Dressrosa for beating Pica.
Even if Pica can do all those things, that still invalidate the argument that Zoro's bounty was given on the sole basis that he wiped the floor with Pica, as such, we can presume that Pica would be seen as a lesser threat than Zoro, and such can be seen as having a bounty probably below Zoro's.
Its not like Zoro dealt with Pica through trickery, he beat Pica through pure force.