People who think admiral are equal or stronger than yonko are just joking right?
Kaido and Teach are main Luffy opponents of major arcs, while Shanks is a foundational character. Looking at the Admirals side, the only major arc marine opponent for Luffy will be Akainu who isn't even an Admiral but ranks above that and definitely can't be held to the same standard as subordinate victims(Fuji&Ryo) and intermediary arc villains that have to share the spotlight with 5 other more significant villains(Kizaru). unfortunately, the majority of the Admirals will be treated like Big mom while only Akainu will be treated like a Kaido or Teach.
This isn't even really a power scaling statement since I do believe overall that Admirals and Yonkos aren't far apart, but it's more about the portrayal of their power, which is ultimately what matters more to power scaling agendas.