Personally, I really like that all of the Emperors aren't just unbeatable, emotionless monsters, but are actually being portrayed as normal, flawed human beings…who happen to be immensely strong monsters, too.
EDIT: Like, it really comes across to me that it's very important to Oda that all of the Yonko are written as memorable, interesting and entertaining characters. Right now, Shanks of all people is probably the most uninteresting Yonko to me.
This is a very important point, honestly. One Piece is about flawed characters (aka better written characters) than perfect ones. If you saw an anime/manga character like, say, Medaka, and you were like "eh, this character is too perfect" (even though that was her shtick), you'd lean more towards preferring flaws in characters.
Kaido got introduced IMMEDIATELY with the "he was defeated x times, captured y times" intro boxes on his first on-screen appearance. So him being unbeatable was never the intention. Just as you said, immensely strong, nearly god-like strength.
Though all of that said, there definitely still are 1-note gag characters but they're usually very minor characters.