Honestly, when One Piece first serialized I don't think Oda ever planned on having bounties exceed the billion berri marker, let alone multi-billions. This is made apparent, as Mr. 3 made a huge deal about Dory and Brogy's bounties. Then you had the introduction of the Shichibukai, with Crocodile at the time being put on the same plateau as Mihawk, but only introduced with a 81 million berri bounty (albeit frozen) but it was in the same ballpark as Dory and Brogy.
I also don't think Oda had planned on making characters as powerful as they have become either. This is made apparent by Crocus, despite being a member of the Roger Pirates, not being that very impressive in terms of strength. Sure you could chalk it up to him being old, and worn down by diving into Laboons stomach acids, but even then, by Prime standards nowadays, he was way to weak even out of his prime. This is also further made apparent by Oda's clear retcon of Crocodiles strength during Marineford. He had to bump Crocodile up to a higher standard, because the powerlevels shifted dramatically since his introduction.
With that being said, if we were to inflate Droy and Brogy's bounties and strength to current One Piece standards, I'd say they should be sitting above a billion berries, and at the high end of the Yonko Commander spectrum, to possibly Top Tiers if they were the Strongest Giants of their time, which they should be.
