Emperors
- S tier. Shanks, post ts Teach, Newgate, Big Mom, Kaido. One on one they pretty much only seem able to lose to each other... they have massive physical and character weaknesses that actually get exploited just so that challenging them makes sense in story, but they still don't lose.
- several A tier commanders each. Base Luffy is stronger than most underlings and Gear 4 makes for a legit new world fighter, but base couldn't beat Cracker and Gear 4 had help to win that one. The guys who can scrap with admirals, moderate the world's toughest prison, boast undefeated streaks, etc.
- new world allies to bushwhack the shit out of you before you even see the bosses
- waves, thousands of advanced fodder. People good enough to wreck East blue or take high numbers in an outfit like Baroque Works. A strong pirate will wear out just trying to cut their way through.
Oda has pretty sufficiently fleshed out the Yonko class IMO. We're going to see them lose because that's what the plot requires, but there's no reason to believe that an alliance between two out of four isn't the greatest power in the world.