I think people is going a bit crazy about bounties.
For a pirate to cost 5b they need to be not only a top tier fighter, but own an empire and be established enough to raise so much. Whitebeard wasn't so expensive because he was Roger's rival (which I doubt Law is to Luffy) but because of his individual and crew power. Same for the Yonko, they are so high because they are well-established emperors that define the balance of the world.
Even the 1b mark is so far unlikely for a pirate like current Law, who is basically a nobody. Sure, he may become a top tier (I insist, may, so far things aren't looking that good), but his crew is a joke and he lacks any charisma to gather a fleet. Also, the reason why Yonko top subordinates are so expensive isn't just their individual power but their affiliaton to their crews (stated by Oda), so odds are that Katakuri, King, Queen, etc. wouldn't even be 1b+ if not for their captains. Maybe if they actually have a prominent, significant role taking down an emperor they will surpass such numbers, but Luffy tends to take the spotlight so I don't know.