I agree, little Robin is a prime example.bounty only shows how much the WG see you as a "threat". it doesn't necessarily mean you're stronger though.
I think they gave the strongest man in the world a higher bounty than 600 million. If luffy already had 400 million, Whitebeard had something around 1 billion IMO.the bounty is based on: hostility to the government,marines and general public of the world,past actions,reputation etc.
whitebeard probably had a bounty of maybe 600 million purely because he was a powerhouse , but he never made rash decisions etc.
robin , a child had 80 million or something like that (i think), proof that strength only really comes into consideration if they are considered hostile , whitebeard was wise , he wouldnt provoke the WG or the marines unless one of his sons where taken from his ship (hint hint - ace).I think they gave the strongest man in the world a higher bounty than 600 million. If luffy already had 400 million, Whitebeard had something around 1 billion IMO.
your post was a prime example and good explanation as to what a bounty actually isits all about your perceived threat level, Kid had the highest bounty of the supernovas because he would just destroy stuff left and right while luffy and law were on his power level but not crazy and causing as much destruction.