Being a player who spams tycoons (as many of you will know), I'd like to say something about them vs kings:
Firstly, I'm very surprised to see the king being compared to the tycoon (or other promoted specialists). What this shows us is that higher-rated players tend to think more deeply about the effects of a specialist. The King's effect is probably the most obvious out of all, which is probably a reason why lower-rated players stack them a lot. They even look different in the way that all outposts lose their shields, probably creating some psychological effect. In higher-rated play, many people go for other stacks, and even those with kings (even up to 4) are usually not too much of a problem.
Secondly, the tycoon pretty much increases your 'potential' and recovery. Many lower-rated players underestimate the power of the tycoon because it doesn't 'seem' to do that much. Once you reach your cap, what do you do? Actually, that is something you need to learn and to master: How to manage your drillers in an efficient way. Being in many games where I have had tycoon stacks, I find that they are extremely useful for diplomacy, as you can gift them to your allies. MoEs and tinkerers are a good choice, but I tend to stay away from MoEs because they decrease your driller production by an absolute amount of about 16%, which is almost a waste of a tycoon when you're on your 4th one. Sometimes, you need to recognize situations where you just have to wait and play it out. No attacking, just defending. As many other players have said, tycoons are both good at attacking and defending, while kingmakers lack a suitable defense of their outposts.
Thirdly, I have been in tycoon vs king situations. So my way of looking at them is this: for every tycoon, it increases your production by half of your original production. So, if you don't reach your cap, you have 1.5 times as many drillers as everyone else being produced. For every king, it effectively increases your production and your cap by 1 third, but having a king stack also means you have no shields. Against kingmakers, a strategy is to defend and counter-attack only when necessary. Since you recover lost drillers so quickly, it doesn't really matter to you that you lost more drillers than your opponent. While they are still building up their next attack, you can easily recover and even launch a few counter attacks if you've defended well (defending well: you'll have to have to gather your specialists together while defending, it's a characteristic of having a tycoon stack). And, I almost always have at least twice as much production as the kingmaker.
Lastly, most of the time I'm actually allies with the kingmakers. I just ask them if they want to work together, and offer them my drillers to get their trust. Since I produce so much I gift it to them, where it does twice the damage (or something like that) than if I were to use it. Its a great stack combination, kings and tycoons. Its a really great way of making allies, if you gift drillers to them. But in the end, if its just you vs your ally, I've found that tycoons often provide a great foundation for strength, and that other things are simply more useful when you have tycoons than when you have kings (e.g. generals destroy a value of usually about 20 drillers for the kingmaker, while it only destroys 10 for you. And then there's the fact that you have shields on your outposts, etc.
Kings aren't OP
"Imagination is more important than knowledge"
----Albert Einstein