Solving the "elf superiority problem"

[noob]

Pretty much. Learning from someone else produces basically no new anima (absorb some, create some, net basically zero), while figuring out something yourself or transforming someone else's idea into something new is a net producer. Even reinventing the wheel counts as long as behind a veil of ignorance (you didn't know you were doing it or didn't copy/learn directly from anyone). For most wizards (especially), learning a spell from a book or scroll counts as learning, while developing spells for yourself (for PCs, these are the two free spells on level-up) counts as creating new ideas.

That is nonsense.
Due to the imperfect nature of language and due to the way language evolve someone who is unable to "have ideas" would after some time be unable to understand a portion of the new texts without external help due to the fact that very few texts describe the evolutions of language and due to the fact that many connection between words can contain meaning that the grammar and the words together do not have.
It is also impossible to understand the way other people write spells (unless wizard did standardisation relatively to the assumptions of the system) because wizards write their spells fundamentally differently from each other and as I said a text does not contain all the ideas that can be found by reading it.
It is even worse if the text is not written by someone that specifies absolutely everything because for each thing that is not specified (for example demonstration skipping) you are literally unable to find it unless you already knew it from another source.

Not having ideas basically makes basic language nearly impossible(after a while) unless there is some extreme force of stagnation enforcing complete non variance in the language and making so that people who write texts are forced to be extremely specific and to write everything in detail. (or making an assumption of the text magically imprinting with anima pertaining to the contained ideas but then someone who did not understand what they wrote despite writing the same text would have an impossible to understand text for people who are unable to make new anima which would result in many mortal wizards asking someone who does not understand magic to recopy their symbols in order to have a spellbook that can not be read easily by people who are long lived or eternal and other weird shenanigans like books being printed through automation being unreadable for immortals)

You made eternal life not being desirable due to the imperfection of the processes people uses instead of making it be a result of the fundamental mechanics (which is a bad thing if you fundamentally want eternal life to be bad).
And you have not proven how it is bad to become immortal through being a demon if you are a person which does not care about murder (which is the baseline for evil people wanting to be immortal).

Also you did not answer my question: would a lich be able to get the idea to research an assistant after taking a kingdom if they never had an assistant before?

By the way you have proven even more the overwhelming superiority in terms of intelligence of dragons hatchlings: due to them having an absurdly short lifespan they would have an absurd rate of idea creation (combined with their insane learning rate and the ability to generate lacking information out of nowhere proves them to be so much more intelligent than any other creature that measuring this intelligence would be nearly impossible).

also

And you underestimate it. It's more like the vast majority of those who attempt the rite fail. Most don't die (at least their bodies don't). Instead they become the "lower" undead, the wights, etc. Some believe that the Black Lord, who pioneered the lichification rite way back when and is the major source of the knowledge needed to become a lich even now, actually publishes/teaches a limited, sabotaged version instead of the true rite. Just like the current Rite of Blood (designed to create a vampire from scratch instead of doing the whole bite/drain thing which makes weaker versions) is a weakened, distorted copy of the original, which produced the Nightlords of yore.

is incompatible with
"there is enough lich variety to have one pacifist lich"
Because people wanting to become liches and having the possibility to try to do so are insanely rare because you need to be very powerful(like level 12 when many lower levels were already told to be extremely rare), evil (because most people do not necessarily knows that it is possible to become a lich and not drain people to death), think they have the right ritual (which involves a high level of delusion or making yourself all the ritual from scratch with no outside sources in which case it is unlikely the lich would decide "it is a good idea to use a jonthar" and would probably devise another way which might be as much lethal but without that added risk) and also be willing to give up the pleasures of the flesh (which is unlikely if you are evil because let us face it: it is common draw toward many evil behaviours) on top of that you need to be a caster(ex: a bard, a wizard, a cleric, a sorcerer etc) which are also rare.
If you combine all that and make so that most who tries dies then you have like 1 lich every 10^12 people who lives or some other stupidly low value and it would prevent having liches that strand away from the norm too much. (ex: the lich which decided to use a hoard to feed itself)
So you need to make all of the following statements false to get sufficient liches despite the death rate: "High levels are rare", "Most people are not casters", "Knowledge about vampires is comparably rare to knowledge about liches" (because it is a very seducing alternative if you can just try to outsmart a low grade vampire to make it die just after it converts you even if you are likely to fail or to get trouble with higher rank vampires)
That or make so that somehow liches never ever get killed and that the setting had living sentients for so long that the only way for the state of things to be as it is currently would be an extreme force of stagnation causing medieval stasis for such absurd time spans it is unbelievable or that it is just a rule of physics of that setting like "it is impossible to create ideas that advance civilisation beyond the medieval era" or a recent apocalypse.