@S.C.:
This is probably a really stupid and previously asked question, but back in the day, could Whitebeard, Roger, and Shiki be thought of as the original Yonkou? I mean, all three seemed to be the top Pirates of that era.
I could be wrong but from my reading comprehension back when Roger still alive, there wasn't much pirates like these days. There's only pirates versus the marines/WG. There's no Yonkou and there's also no Shichibukai to balance the great power in OPverse. After Roger execution and announcing the hidden treasure One Piece, everyone start to becomes a pirate. Meaning there's more pirates today compare to 22 years ago. The amount of pirates activities increased.
That's why WG hired a certain pirates as Shichibukai to take care of the newbies in Grand Line to control the pirates activities. Hence why wuss like Don Krieg couldn't survive the terror in GL after encountering Mihawk and decide to retreat back the the East Blue. Note, one of the Marines motives (other than the keeping the void history forbidden/taboo topic) is to end this pirates era. Shichibukai and Yonkou are there to stop/control the amount of newbies/amateurs pirate. Although they both are doing it not because of the marines says so because some of the Shichibukai take it as a fun job while Yonkou is showcased what a real, veteran pirate is capable of against those amateur pirates.
To put it in much simpler way, more pirates activities equal more jobs/headache to the Marines HQ. So, I doubt there's a power balance back in Roger's era. There's no reason to have it since not everyone is interested to sail to the Grand Line and the New World unless they are looking for something (One Piece).