Your puzzle-cube dude is obviously not a Kingmaker, and I'd do my best to wipe the bastard out too

I'm not really sure that I thought everything through. See, part of what makes Kingmakers so incredibly evil is that it's only worth caring about them when you already have the lead. If someone is outstripping you in prestige, that guy gets your attention, not the Kingmaker. The military guy, the guy without PoPs, that spent his opening moves carving a hex two spaces from your stronghold rather than going for PoPs, that guy gets everybody's attention. Because he's not just gunning for one of you-- he's gunning for all of you. And that's different.
But the Kingmaker is just gunning for one of you. You never have to worry about him unless you're the leader, or unless you're going for second place. In the early game, sure, there's that guy you suspect of it, but there are more pressing demands for your attention. Forcing blood feud with the one guy that never levels any demands your way is not a priority, and this is, if anything, a game about priorities. The fact that it might not be you always leaves him second in your true, personal threat ranking.
The prestige cost is a small part of the problem with the Unveil Kingmakers event. Yeah, it's significant. The bigger problem is that, if I'm not mistaken, it does nothing to defang any unveiled Kingmakers. They are still not the biggest threat to anybody but the leader. In fact, playing the event when you suspect a Kingmaker can cost much more than the prestige and the order slot the event needs.
There are random elements, there are political elements, but in many ways, SI is a game about knowledge. I'd like to introduce an (arbitrary) division between two kinds of knowledge: what you know; and what you know they know. If you've engaged in a blind duel against somebody you've engaged in bidding wars for manuscripts, you know what I'm talking about. It's not just a matter that you know you'll be facing a praetor trained with veil of smoke; it's not just whether you know that your impenetrable stance manuscripts should net you the win. The question is, do you know that they don't know you have impenetrable stance?
If you know that there's a Kingmaker, and think they want you to win, the last thing you ever want them to realize is that you know that they're a Kingmaker. Before they think you know, they'll help you, if you're their target, in all sorts of ways that are beyond your ability to divine. Afterwards? They'll do everything they can to convince you that somebody else is their target. And that means screwing with you, not only in their basic, prestige-nullifying way, but in every way. Your only defense against a Kingmaker is military, and they know that. Before you know, they'll lose a vendetta for you. When they know you know, they'll do everything in their power to prevent blood feud. And so, this public reveal, which sounds so nice, doesn't end up pitting every other player against the Kingmaker, like you hoped it would; those people are still gunning for you, or, likely, trying to plan their military victories, now that you've emerged as the prestige leader. Instead, it's robbed you of an ally in the form of the Kingmaker, and launched the Kingmaker into full-on defense.
Now, I want to make clear, this is mostly all just theory and fever, originating more in meditation than in experience. It's true that players adapt as things progress. But not everything changes, and I think that winning play adapts towards winning strategies. I don't think it's a (consistently) winning strategy to risk a 20% chance at a win, by sacrificing valuable early-game resources and orders, in order to prevent a 20% chance of a spoiler of that 20% chance of a win.