But the sovereign is the focus of the game. He's *Me*, so to speak, in the game. He's the one going around founding a kingdom. He's doing quests. He's the all powerful magical channeler badass guy...
Yes, absolutely out there doing Quests, marching into Enemy territory? Not often. Kings were not commonly on the front lines, there are a few exceptions to this rule (for instance Richard the Lionhearted), but they were soldiers well before they were Kings, and in virtually all cases they were incredibly poor Kings.
And he shouldn't go anywhere near enemy territory. WTF? It's lame and not fun.
Why is it not fun? There's a lot of other things for the Sov to do. Questing, for instance. Patrolling the territories of his Kingdom. Adjusting the terrain within the Kingdom. You're still marching around attacking stuff, so the fun is still there. The fact that your Sovereign isn't physically in enemy territory doesn't make him useless. Hell, take the city with a Champion, garrison the city with your King to fight off the counter-attack. Lots of different things you can do.
This goes one further if they add in that spell that closes off retreat points, by the by.
The sovereign should be one of the strongest units on the field, leading the charge. Not sitting back in the capital because it's cozy and actually fighting can result in game over. I can't even begin to describe how much fun is sucked out of the game by that mechanic.
He is the strongest unit on the field, that doesn't mean he should be leading the Charge. Eisenhower didn't fight on the front lines. That sort of thing is lunacy. He has Generals that lead the Charge (aka Champions), the Sovereign has other matters to attend to that are just as fun (in some cases more, like Quests), and that doesn't require him sitting back in the capital because it's "cozy".
The sovereign can't be everywhere, so once we're at a point that having multiple stacks out at once makes sense it won't be as big of a problem.
Outside of your territory, you are correct. Inside of your territory: Build more roads, then he sure as hell can be everywhere at once.
Champions aren't worth hiring because the cost and commitment required to power them up is so much greater then the cost of a bunch of guys with Lord Maces who can simply one shot said champion, and the bunch of guys are much easier to replace. When the attack/defense mechanics are fixed, champions should become a lot better then they are right now.
Yet if you had no Organized or you were up against a human player that wasn't using Organized, this benefit that you're seeing would be lost, because you would have one big army and he would win a war of attrition. Which is my entire point with that whole post -- Organized narrows your strategic options, not being Organized widens them and gives you a more robust strategy.