Being a dominant alternative to Province isn't really an issue for 8$ cards. If "what do I do with my 8$" was supposed to be a meaningful choice, virtually every kingdom ever used is bad and most of the recommended kingdoms are bad.
Cards like Colony, Prince, Platinum, Goons, Tournament, Nobles, and Forge pose more of a question of, how significant are the moments I hit 8, and how do the contents of my deck matter differently when I start to hit 8? They are more like rule benders than items on a menu that are there to present a meaningful choice. They are brutally dominant a lot of the time, and that doesn't usually upset us. The decision price points are 3$, 4$, 5$, and sometimes 6$ (it's often ok if we lose that one). 6-8$ cards tweak the way we evaluate 3-5$ cards by their presence in the kingdom rather than presenting meaningful choices themselves. "Is Navigator better than Militia when I can accelerate an incredibly early Platinum? Is Smithy a stronger opening than Plaza even though I know Nobles will be coming into my deck this game? Baron spikes are good, but don't I need a more sustainable way to hit 6$ over and over to reach Goons critical mass? Or is the trashing enough? Why can't Baron be obviously better than X like it usually is?"
King's not different from that.