I've noticed that the term "admiral level" is always used when people are describing someone they think is lower than yonko, this is a form of downplay that seperates the admirals from the highest tier, where they truly are, alongside the yonko.
In marineford, we see the Admirals fighting on par with whitebeard, the strongest man in the world. Oda even showed us that whitebeard and shanks were equal standings when they clashed and the clouds split evenly. Even if you want to downplay whitebeard to the weakest yonko, he definitely still yonko's level. It's an extreme difficult fight for any of the other yonko to defeat him. Saying anything else is blasphemy.
