Nailed it. I have about 230 hours, not much compared to many. I started my second play-through just a couple days ago, and suddenly last night I started to feel "whats the point?" Stay bored with looter and bandit battles before joining a kingdom, or join a kingdom and suffer through the awful AI decisions, get a castle or city and then constantly defend it until the kingdom makes peace. In about 30 mins of play my first castle changed hands 4 times. As a new character I'm around 70 troops hopelessly left to abandon a siege of 1200 plus, and hope my AI armies choose to back me up. They don't...they just went to a new target, lost... and got 6 lords captured.
Progress is kind of an illusion in this game. And consider how easily you can screw something up or get yourself into a situation where you are stuck (i.e. being given a fief that is on the brink of revolt, starving, and no prosperity). On my first character, being king really didn't change the game at all for me except giving me final say, only to have my decision to make peace for example, pretty quickly undone. Enhancing the army strategy feature a bit may help. As king the player should have a bit more agency in deciding where armies focus their efforts, because currently they are nothing short of idiotic. The first army I joined after joining a kingdom lost a battle we highly outnumbered the enemy simply due to really bad tactics. No archers on high ground, cav just sitting still under a rain of arrows, and infantry standing downhill from enemy archers making their shield wall highly ineffective. It's just very frustrating at times. Especially when the only hope I have to retain a castle is to dump most of the troops into a garrison just for a prayer of keeping it. Then the boring routine of making the rounds to recruit more, in which time the inevitable siege will come. Kind of made me want to abandon my new character for the original one with 400+ troops, at least able to defend my own land, even if that play-through feels its done with a little over 50% of lands conquered. Despite high relations with lords, and many attempts not one has joined my faction leaving my nation unable to properly govern or defend new lands. And constant war on 3 fronts begins to feel like a stalemate of give and take.
Everything in the OP was very well stated. And it caused me to really in an instant go from "man I love this game" to "what is the point?" I could always just make my own custom battles if I wanted endless combat under interesting conditions, leaving me to agree that the non-combat aspects of the game are incredibly lacking and in some cases non-consequential.