Even if he rivals Blackbeard in strength, I doubt it, that alone wouldn’t get him 2 billion berries because he has no crew or influence. He’s literally just a swordsman.
1.8 is very generous
You seem to look at him that way because we have only seen the Mihawk who doesn't want to be bothered. That,'s a reason why he became a warlord.
Like I just said, we don't know anything about his history other than he sought out strong swordsman until there was no one left the challenge.
Remember when Don Kreig bothered him. He destroyed all his ships except for one who he later destroyed. Now picture the Marines interfering his dual when he was trying to become the strongest. I can see that Mihawk attacking and destroying hundreds of marine ships with ease.