Before Pirate age? You mean that at the 23 years he was already strongest and that's why fight against YC lvl Shanks? Oh, wait...
WB and other Younko got that title due the fact that they was opposite to WG and just couldn't be ignored, while Mihawk was WG part of force, so it is strange that every Marine was hyped about him in MF and surprised, while he was blocked by Jozu YC.
Fact is that Oda will never reveal plot twist about fact that Mihawk never was Strongest, while it was Saitama Gorosei, so instead he just continious to reply about WSS Mihawk, while in manga showed already that Mihawk isn't even that powerful case WG don't need him, and WG will never threw into the garbage Younko lvl dude, or Admiral lvl.
Now speaking about bountys, due fact that Luffy was called as 5-th Emperor with 1.5 billion we could clearly see that no one except Younko break threw this limit(1.5), which lead to conclusions that no one except Younko got 1.5+ bounty. Why? Because if there was like a lot of pirates with bounty 1.5 b+++ those Morgans Luffy ype wouldn't have any sence.