Campaign concept derailing

[Resileaf]

I've been GMing a long-running campaign (half because it's a long campaign itself, half because we've sometimes had months of no playing due to schedule conflicts) which started as a very political campaign set in an Empire on the verge of falling into a civil war and collapsing upon itself from the pressure of outside invaders. With one of the players being a noble owning a castle and the other players being his retainers and personal friends, the intention was that he would be thrust in a world of politics and backstabbing and managing his estate and army as war becomes inevitable and he has to carefully choose his alliances. Furthermore, there was a level cap of 5 to give the campaign a slightly more realistic and balanced feeling, so that there would always be a sense of danger involved (a level 5 character can be overwhelmed by a mob of peasants if there are enough of them). I wanted to give the campaign a Crusader Kings 2 kind of vibe.

Unfortunately, the player who was elected to become that noble is a wizard shut-in with no social skills whatsoever. It's been a struggle to make him involved in politics, because he never had any projects, never tried to involve himself in the politics of the Empire, and generally focused on staying out of things. Which is understandable, there are neutral parties in many wars, and he was courted by the parties involved to try and gain his support. His family also had a rivalry with another noble which was intended to make for a long-running conflict between them.

To make a long story short, I often had to force alliances on him through coercion and kidnapping of his family members to make him do anything, and have given up on the low fantasy concept by adding further outside threats to keep things engaging because he decided that he only wanted to focus on what was outside rather than inside the Empire (the main threat was an orc invasion, so he refused to participate in the political game under the justification that there were more important things to take care of first). In turn, I've added: The wood elves are being mind controlled into hating humans and desiring their destruction by a druidic artifact; barbarians from the north are invading; the undead are rising in the southern deserts; drows and duergars are attacking the dwarves; a dragon destroys the armies of several factions while they are locked in combat; demons have covertly taken over a city.

So obviously, my initial concept was derailed pretty badly by my attempts to give my players something to do, and the low-fantasy world has turned into a high-fantasy world with low-capped characters. In my attempts to salvage things, I've given my players the option to play a second group at the same time, who would themselves be adventurers trying to do the things that a noble couldn't do. As such, the adventurers have become much more important to the campaign than the nobles themsleves, because the nobleman was disgraced when his inaction caused the entire population of his castle to be massacred and his position as head of the family was taken over by his younger brother. This means that he is no longer part of the political world and has become pretty much useless.
I'm thinking of dropping the noble group entirely and focus on the adventurers and make them hunt down a single objective that will result in one of them ascending to godhood and breaking the level cap for the entire world.

So, um, with all that ranting done, I kind of would like opinions of where I went wrong, how I could have kept things from devolving into such a mess, and if my objective at least has a chance of giving a satisfying end to my campaign. I understand that I might have gone rather confusing here and there, so if there are parts you guys would like me to elaborate on, please let me know.

Edit: I just now realize I should have probably posted this in the meta forums rather than those specific to D20s. Should I repost it there and ask for this one to be deleted or some such or might as well just leave it here?