Oars Jr had a far bigger impact on the actual battlefield than someone like Squard, so Oars Jr's bounty is definitely justifiable(considering he was called a monster even by someone like Sengoku).
All the big boys - giants, yeti cool, punk hazard children, dragon Kaido etc - are able to make big impacts. They can level cities which not even Shanks does easily. But they are at the same time big targets and often slow as Doflamingo showed. The Speed problem was solved for Morias Oars - a super Giant with Luffys Speed and bouncyness.
So yeah, for the average pirate or Citizen the big boy is the larger threat and 550 is justifiable but if we go by strength at the top they are often quite small but pack a punch like Luffy, Shanks, Rayleigh, Mihawk etc.
Squardo should have been the equivalent to Jinbei in Big Moms crew or Doflamingo in Kaidos - i.e. the strongest allied captain but 210 doesn't really reflect that.