True, you can argue that. But party size can also be increased with renown, which can be easily grinded. Using your companions means that you are missing out on unkillable, monstrous custom killing machines and relying on your companions not getting shot in the face during a battle. If a battle goes awry, you can be potentially crippled for a week and lose your entire army. I can ensure my own welfare far better than that of an AI companion. Eh, different strategies are what make M&B a wonderful game.
How do you grind your renown? Because AFAIK it's mostly fighting armies larger than your own, which... kinda goes against the entire point of the exercise.
Also, double companions per skill.
INT points, for me, are way too often just redundant and useless.
The unkillableness of companions is not much of a factor with my playstyle, because I tend to have absurd-level Surgery, effectively making 90% of my army unkillable, and I really hate micro-managing my companions upgrades and spending a zillion denars on making their gear not hoover anuses.
Plus, the losing your entire army aspect is fairly null and void if you can raise and train the whole army back into shape in a week.
You kinda need a zillion denars to train up and maintain a 120 strong man army, and as you say retrain you still gotta pay for all those. Completely ignoring training renown makes it extremely hard to maintain your own kingdom and get good lords you like.
You might also have forgotten that completely losing a battle makes you lose most if not ALL of your companions, good luck finding the idiots again. I can agree that once you are off your feet and in a relatively stable position with the right companion match ups then it would work, but it requires loads of micromanagement to find, level and keep them. Also, you can tell me that it is null and void when within that week you lose 2-3 castles, which is entirely possible.
I completely disagree with the notion that you lose your killing ability by focusing Int. Str/Agi don't really give that much benefit, since I can easily get 1 hit kills with 8 Str and 10 Agi with a Charger/Lance, or any other quick 1 handed weapon. Sure, you might be a bit faster or have that much more healthpoints, but that can be easily fixed with armour and effective blocking. In a siege, a siege crossbow with steel bolts will slaughter anyone, period. I can negate the loss in skills and attributes with the right weapons and weapon proficiencies.