Honestly Yonko only received more hype from fans because of how WB looked GLORIOUS in Marineford
Admirals were always the measuring stick in this series I feel...
If I have to describe the difference between Yonko/Admirals
I would say:
- Admirals are the BEST TRAINED FIGHTERS
- Yonko are the most GIFTED FIGHTERS
In other words, if you compare it to a series like Hajime no Ippo:
- Yonko would be Bryan Hawk
- Admirals would be David Eagle
To explain:
- Kaido/Big Mom: Born as natural disasters, Tough Skin/ Impenetrable... THEY NEVER WORKED HARD for it
- Blackbeard: Born with SPECIAL BODY, that allows him to eat more than one DEVIL FRUIT
- Shanks: A snitch talent, LOL, for real though, King's supreme Haki is a GIFT/Talent he inherited...
Admirals:
- ALL OF THEM, are kinda the same, they are the PEAK of what a normal person like "Koby" would achieve when he reaches the maximum level... They are basically what Yuri Boyka would say "Most complete fighters" in the world... which is why you can see that ALL Admirals apply advanced Haki/Ryuu, and some of them showed signs of Future sight like Aokiji/Akainu...
And I think WB/Roger are a combination of BOTH:
They are Naturally Talented/Gifted people, BUT ALSO, they have TRAINED THEMSELVES to be complete fighters JUST like Admirals... which is why they are so advanced... which is also similar to the journey Luffy is following... Luffy is really naturally GIFTED from Garp/Dragon Bloodline... with special talents... but also, he just like Admirals in that he trains ALL Haki types to reach MAXIMUM potential