Not sure I understand "rightful liege"

[runs_with_scissors]

So I'm emperor, and hold title to 4 kingdoms. But because I haven't created the duchy titles, I'm not their rightful liege?

[Admod, the Equivocal]

That's right. The duke in the north is the only ruler for the men of the North. No 'emperor king' will do. Only the duke in the north!

[EA Latium]

Precisely, as there are different "steps" in between, that may happen as well with your Dukes and Kingdom Titles within the Realm.

[runs_with_scissors]

I've got 12 duchy titles I haven't created... Is it worth it? Anyone know what the tax and levy penalties are for not creating the duchy titles?

[Admod, the Equivocal]

I don't think so if you have no plans on giving out the kingdom titles.

[EA Latium]

It's definitely worth it, you can check how much of what they are giving you. Anyway will be much better in the long run, the less direct Vassals you have to manage the better is normally, so even handing out the Kingdoms Titles could be very useful.

Keep in mind you'll have a succession sooner or later, one thing is to keep let's say 10 Vassals at bay, another is to keep 30. It's also better for managing their individual contracts, for example you can have some more focused on money, some on levies and then the various "special" titles like Scutage and Palatinates.

[Lofwyr]

The tax/levy calc. is mostly based around your domain limit. If you are over your domain limit, you can select a County and view the tax/levy numbers, and it will show you the malus you are attracting.

Creating a title can give you a nice renown boost.

You can also only hold 2 duchies. Anymore and you start to earn a negative opinion modifier with all your vassals (they are jealous).

If you have that many un-created Duchies you must have a large number of direct vassals- there's a cap to that which you can run into shown on your domain screen. Furthermore, all those Counts etc. if they are deemed powerful, will want to be on your Council...generating further negative opinion if they aren't.

It is far easier to manage vassal opinion by setting up a decent pyramid structure, and handing off all the low value territory and their Rulers to Dukes. Then you only have to keep the Dukes happy.

Eventually you can do the same with Kingdom titles and the Kings.

You can even cherry pick who to give the Duchy title to if its newly created, allowing you to pick a ruler with a decent stat to be on your council.

Lastly, by having powerful vassals, and high crown authority to prevent them fighting each other, you should see your vassals attacking other rulers and expanding your realm for you.