"as for Buggy the Bombastic Clown, considering his formidable pedigree and the fact THAT HE GOT THESE TWO TO YIELD TO HIS AUTHORITY"
See the CAPSLOCK part?
It means the bounties are post Cross Guild formation. It also means that Mihawk's bounty is his bounty as a member of Cross Guild. Remember, being in a Yonko Crew can increase your bounty by default.
It's not his strength alone.
Now, if you wanna argue that "being in Cross Guild" is maybe responsible for the 90M, while the 3.5B remaining is purely for his strength, etc, well, good luck with that.
That is a much stronger indicator than your speculation that Mihawk's bounty is inflated by his presence in Cross Guild. The manga disagrees with that speculation.