Are they exceptional heroes, or some random you picked up for less than the price of a lame horse in a local tavern?
Think of your companions as your most trusted advisors and specialists. They fill a specialised role. Do you send your best scout into the front line in a battle? Or your best doctor? or best engineer? No. you send your grunts.
Realistically, an historic medieval era army had many non-combat roles, or specialised combat roles. Armies had payroll officers, accountants, architects and engineers, surveyors, cooks, all manner of logistics officers, plus a million different camp followers and clingers. Armies are about more than just grunts.
My companions get into the fight when needed. That doesn't mean treating them with kid-gloves, it means respecting them. I treat them like I treat my character. I don't charge the front line solo at the opening of a battle. I attack when an opportunity arises to maximise my impact, my character is better alive to command. I group my companions together and use them as a mobile reserve. I can place them where I see weakness in my line. They are all mounted, and missile armed - which makes them great to sit in behind the front line, killing any cavalry who break through.
It's a respect thing.
Oh boi.
What is it good for, when characters best suited for role of a captain, are left behind, with few others , just to idly guard your back lines and throw spears when enemy gets close enough? You talk about respect and yet they cower behind your troops, which is exactly oppossite of what would a feudal want by the way.
I value my companions, yet most of them were trained to be captains. I can understand your approach with archer captain. Sure, he has nothing to fear if you can manage your army well and control the battlefield. But my infantry captain, whole different story. She is there to give my ranks advantege in man to man combat, and if the enemy charges your lines, who do you wait for to stop it. Well I guess you try to put archers behind your infantry, right ? And it's the infantry captain that is suddenly in grave danger. It's either to risk her, or to risk everyone else.
Had this glorious battle, which allowed me to besiege a castle or a town undisturbed and unopposed, I don't really remember what it was anymore, but among casulties there was my infantry leader. After few attempts I quit playing tbh. Even tho I could propably take the settlement and have better immediate reward. But I don't want to trade a town/castle, that there's a possibility I won't even get from that poor bloke Alary, for life of one of my experienced, equiped, skilled, valued and "trusted" followers I had since almost the start of this run more than half a year ago, and as you said, are exceptional. It would be certainly a loss in a long run.
But tell me, why is there the option then, obviously intended one, to put them in charge of a fighting unit?