Firstly there's 3 Admirals at a time unless you're counting Fleet Admirals who rarely fight because of their position. Secondly if that were true then why need to call in all 3 Admirals and all remaining Shichibukai when threat of 1 old dying Yonkou is coming? As strong as Akainu came across at MF nothing really showed or implied that any of those Admirals would have beat WB had it been 1v1 from the start.Admirals DO equal Yonko.
How many Yonko are there? 4
How many Admirals are there? 4
If the Admirals don't = the Yonko in a 1 vs 1, then who is there to keep the Yonko in check and provide a balance? NOBODY. So the whole crap about Yonko being a tier above the admirals is BS.
Shanks has never shown to be stronger than the Admirals.