Titles are the most misunderstood thing in One Piece.
We have a POSITION title, and we have a POWER title. The position title would be like Admirals, marines, bartender, chef, Pirate King and so much more. While a Power title would be like the World's Strongest Swordsman, World's Strongest Creature, World's Strongest Man, World's Strongest Criminal or World's Strongest Weapon. If someone is given the title of an admiral, it would mean their position are really high in the WG, and if it were a Shichibukai, it just means they are pirates who work with/for the WG, which doesn't necessarily equate to being powerful to a certain extent, or not. In other words, titles are taken very seriously in One Piece. Only thing some people do is conflate between a Position title and a Power title by making them the same thing. An Admiral level, may just be a form of general expression for someone who is really strong but not necessarily that every admirals is the same, or that they are more powerful than a warlord/Yonko/gorosei. Likewise, the warlord's powers may differ from one another. So for us to say, Mihawk is just a "warlord" level would be like if we were to say Mihawk is just as equally powerful as the other warlords, which we know, is not true, based on countless of evidences from manga/SBS/vivre card.