Then it's simply as I suspected.
Your entire concept of "balance" is just skewed and warped to player-convenientism.
I'm not trying to denounce you our anything. I just want you to think about this.
Let's say a game gives you a choice in the beginning, to:
(a) Play as a powerful lord or king
(b) Play as a middle-sized noble with limited resources
(c) Play as a commoner, bound by duties
(d) Play as a beggar, no possessions, in debt, impoverished and weak
Naturally, anybody would expect the relatively difficulty of the game would be the easiest with (a), and it would get gradually more difficult with other choices, and (d) would feel extremely difficult. The game gives you a life to choose between (a) ~ (d) and that is sandbox. In this instance, you are saying you want to play in the way of (c) or (d), but then you are also complaining that the difficulty is much higher and punitive than when you play (a) or (b).
So, your concept of "balance" is that you want (c) or (d) to be as easy as (a) and (b), and so long as (a) and (b) is easier, you criticize that the game is limiting your choice and failure in balancing.
That's just plain wrong, man.
A good example is Crusader Kings II, THE medieval sandbox game. The most common and easy choice would be start the game off as aking, or at least a Duke. But you want something different, so you go for an Earl, stuck in a backward quadrant of Europe, low tech, low developments, realm bordering with Muslims that constantly invade and conquer, and your lord hates you and keeps conspiring to take your land. You seriously can't expect the game to be just average in difficulty when you've on purpose, picked a much more difficult spot to begin the game.
Stuff like bows, mounted archery, and hiring recruits is the same. It's the most standard and easiest way to do it. It's probably also the default standard when the devs determine the game difficulty. But if you throw all that away on purpose, and just want to solo, then you're willing taking in the greatly increased difficulty of the game as part of your journey. Why are you complaining about it?
(ps) For the record, I play solo for around the first 5 years of the game, because I want to strengthen my character before he/she really jumps into politics and war. I don't use mods, cheats, trainers. Yes, the game's difficulty is quite increased, but it's not insanely impossible at all. It's not unreasonably difficult, but fighting solo will bring its penalties in stuff like limited cargo load, limited volume of trade, and always choosing carefully the battles you can fight and win.
It's doable.