WG has 4 admirals but luffy won't be defeating all of them. He won't even defeat all gorosei.
And, series is near its end is bad argument - because this shit is nowhere near getting wrapped.
Another thing - luffy always end up getting extreme diff fights - he isn't beating an admiral mid diff - that too when it's first admiral to go down
Neither Caesar nor Hody were extreme diff fights lol.
And admirals always fight nerfed dudes...and still barely win.
It's not just marineford.
Oda had to nerf Garp for Kuzan to stand a chance.
Why would a prime yonko be challenged by a lone admiral?