When Big Mom speaks of her possible alliance with Elbaf, and what she would be able to do here is what she says
So the general idea here is that :
Bigmom+Elbaf army > Whitebeard > Kaido/Shanks.
She doesn't mention the Marines or WG, many Yonko fans use this as an argument to say the Marines are irrelevant yada yada.
However when BIGMOM allies herself WITH KAIDO here is what their COMMON GOAL is
Suddenly the WORLD GOVERNMENT and MARINES become relevant now that she is allied with KAIDO and plans on taking the ANCIENT WEAPONS.
The reason why she did not bring them up when speaking about her alliance with ELBAF is that even with such power, she would've been UNABLE to do anything against them, despite crushing the other Yonko.
So here we can get a clearer picture of how the balance of power works in a Yonko's mind.
In Kaido/BM's heads : 2 Yonko + 3 Ancient Weapons > World Government > 2 Yonko > Yonko+Elbaf > Whitebeard > Other Yonko.
(Keep in mind that Yonko are arrogant as fuck, so it doesn't confirm 2 Yonko+3 ancient weapons can beat the WG)
In other words the 1 Yonko=Marine+Shichibukai nonsense is debunked by the Yonko themselves, they only consider attacking the WG if they are allied AND have ancient weapons.
With Elbaf power they only consider taking each other out