I've decided to write this down since King Kai's role was quickly overshadowed by the Supreme Kai, Shin, who himself was turned out to be just a "youngster" (that's why the Old Kaioshin got created), clumsy and inexperienced/not fully grown into his position.
I am fully aware that Dragon Ball has this tendency to replace the supreme force in the universe as frequent as Goku surpasses into a new realm of power, but wasn't it a "bit" too rushed by Toriyama to jump from the Grand Kai's level into Shin's without giving the old chump a bit of a definition? Kami was Earth's guardian and till Goku's 1st death against Raditz he seemed to be the "top dog", then we discover that he's actually nothing in comparison to King Yemma whose job is to oversee the souls advancement into the afterlife, Yemma is of course nothing in comparison to King Kai who "governs"/monitors the North Quadrant of Universe 7 (we knew him as the "highest ranking guy" Goku and the Z-Fighters could consult with till the end of the Cell Games Saga), and there are 3 others like him for each other quadrant (I still don't buy the whole DBS "there are just 28 plants with sapient life on them" Shin line before the Tournament of Power, the guy wasn't even aware of the existence of God of Destruction's role till Beerus showed up), then we ran into the Grand Kai who is just a rock n' roll, cars and fighting tournaments loving dude who is in charge of the Kais and allegedly monitors the universe (4 quadrants in lower resolution) from the position above them.
But that's all we know about him, he served no purpose. Then the Kaioshins appeared and allegedly they're the "top dogs" who set the foundations of life around the universe (not sure if they can create planets though), but then we discover that they're just in "tie" with the GoD who destroys the lesser worthy life forms to maintain balance in the universe, and who is subpar with his Angel, Whis, who himself is in awe to Zeno's bodyguards and to the role of his father, the Grand Priest, who is "just" Zeno's "babysitter/educator", as we can say for now.