There is no difference between the strength of an Admiral, Fleet Admiral or Yonkou as a collective group when considering average strength; simply put: they're all on the same tier (more or less). A Fleet Admiral isn't always the strongest of the Admirals, and Yonkou aren't always the four strongest pirates.
Perfect examples are when Kuzan was nominated as Fleet Admiral and yet Sakazuki has since shown to be superior in strength, there is nothing except our opinions to judge whether he is stronger or weaker than Borsalino, Ryokugyu and Issho. There is simply no substance in the argument that the Fleet Admiral is always stronger. In fact, Garp (whom wasn't even an Admiral) is commonly regarded as the strongest Marine of recent times.
The Yonkou obviously vary in strength, from Shanks; whom could stop one of Sakazuki's attacks without too much trouble to Blackbeard whom probably still wouldn't force an Admiral into a high difficulty victory. Their title is determined by their influence politically, economically, socially and strength wise. It's not just based on strength. This gives rise to the possibility of other Pirates we haven't heard of yet being on par with some of the Yonkou. In fact if it was just based on strength then there would be no Blackbeard, Mihawk would likely be a Yonkou instead.
Perfect examples are when Kuzan was nominated as Fleet Admiral and yet Sakazuki has since shown to be superior in strength, there is nothing except our opinions to judge whether he is stronger or weaker than Borsalino, Ryokugyu and Issho. There is simply no substance in the argument that the Fleet Admiral is always stronger. In fact, Garp (whom wasn't even an Admiral) is commonly regarded as the strongest Marine of recent times.
The Yonkou obviously vary in strength, from Shanks; whom could stop one of Sakazuki's attacks without too much trouble to Blackbeard whom probably still wouldn't force an Admiral into a high difficulty victory. Their title is determined by their influence politically, economically, socially and strength wise. It's not just based on strength. This gives rise to the possibility of other Pirates we haven't heard of yet being on par with some of the Yonkou. In fact if it was just based on strength then there would be no Blackbeard, Mihawk would likely be a Yonkou instead.