No matter how strong or weak you think Rayleigh is compared to the other old era characters, no one can deny the fearsome reputation he has in the one piece world. Everyone has a hypegasm whenever he appears "OMG ITS THE LEGENDARY DARK KING RAYLEIGH NO WAY". A legend written in so many books
"Do you want the marines to take on 2 legends at the same time"- Garp calling Rayleigh a legend alongside whitebeard
Recently even yonko blackbeard ran away from him
But it's not just his reputation, Rayleigh has been very relevant as well, being the person to save camie in shabondy, protecting the strawhats from kizaru, teaching luffy haki, accompanying him back to marineford and seeing him off, saving boa and driving blackbeard away
However, when we go in to flashbacks and see rayleigh in his prime, all this hype and relevence seems non existent. Oda shows Roger clashing with Whitebeard, Roger and Garp taking on the rocks pirates, oden fighting kaido, shiki escaped impel down and fought garp and sengoku, but where is rayleigh in all this? who is rayleigh fighting? Oda doesnt even bother drawing rayleigh in the battle with rocks...
So why is rayleigh called the dark king? epithets aren't created out of nothing, there has to be a reason. For example, knew garp was called the "hero of the marines" back since chapter 423, but we only found out
why he is called that hundreds of chapters later when he got lore about rocks. That's why I think rayleigh must have done something to be known as the dark king, which hasn't been revealed to us yet. It definently feels like something is missing. If there really isnt anymore to rayleigh than what we've seen then all the hype surrounding him just doesnt make any sense