You don't have to give the land to all of them, just to the unhappy ones.
Also, gifts.
If you keep all of the Dukes as direct vassals, you might be able to deal with the unhappy ones, but someone will rebel for sure when succession pops up. Except you keep dozens of thousands of gold stored, you simply won't have the resources to bribe all of them immediatly; a King is ultimately little harder to satisfy than a Duke, but it is fairly common for an Empire to have four or more times as many Dukes as Kings.
I suppose you're right that they aren't threats.
But regardless, it's still easier to deal with a lone duke rather than a king, both time wise and manpower wise.
True, but if manpower is no longer a tangible issue why would it matter?
That's assuming you want to give your heir land. And assuming you don't have more kings that hate you than land.
Wheter you want to or not doesn't matter. We've been talking about what is most efficient, not what a given player might like best. Likewise, as I've said before, it is trivial to get enough land to keep a dozen or more Kings happy, at least for as long as there are heathens for you to conquer.
I'm not arguing if an AI can beat your army, I'm arguing about if they somehow did. Or your army got eaten up by attrition. Whether they can or cannot, is besides the point entirely.
"I'am arguing about if they somehow did" - if they cannot beat my army, what'd happen if they did doesn't matter. Likewise, attrition isn't a problem because you only have to dispatch a meager fraction of your army to deal with a rebellious King; a player can beat the AI with an army much smaller than theirs, when the scenario is inverted, it becomes a massacre.
While you can press for kingdoms at a time, you could run into situations where there are fractured kingdoms or where there are no claimants that want to come to your court. I've often struggled to find claimants that wanted to come to my court.
You can bribe said claimants to facilitate the process, but I must concur that sometimes there are simply no usable claimants to be found. Still, for the purpose of this argument, a valid claimant for every christian and orthodox nation is likely to have appeared before you manage to annex all of the heathens in the map. Failing that, what few claims you didn't manage to put your hands on can be substituted be covered by marriages, pressing lesser claims and usurping titles.
Yes, often they do have to hate you in the first place. I'm pretty sure I've never said otherwise.
No, but you took such a fact for granted. If you let all of your vassals' disposition towards you fall into the negatives, you are already at fault.
I doubt it. If the RNG somehow gives your heir's heir crappy traits, kills your heir, gives ALL of your vassals Ambitious and then they start plotting but refuse to stop or you never find out the plot, and then you have 90% of your kings revolt for a claim on your throne, I question if it's still within the player's ability.
Everything prior to them starting to plot is, indeed, outside the player's control; however, my heir's heir would have access to both my direct holdings and those of his father. Unlike Dukes, the number of Kings on the map is limited and there are only so many individuals I'd have to satisfy. I might have to temporarily open hand of demesne, true, but you'd still be capable of offsetting the disposition penalties through bribes and granting titles.