I think this is the perfect moment for mentioning something "bigger", which I think still is missing to balance the game totally: infantry balancing. (I posted this somewhere before, but I can't find it any more...

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Especially on sieges, but also on open fielded battles, you don't use infantry that much. In fact I don't, ad why should I? There are two ways to fight: with arrows or in melee. For the first one you use archers, and for the second one nothing is better than cavalry. Infantry actually has got no purpose. Why is that?
Because of the cavalry. Infantry and cavalry don't add to each other, cavalry is totally dominating. It's top-tier infantry with superior equipment on mighty horses. So you can either have a totally devastating force on the open field, or at least some heavily armored top tier infantry in sieges with only one troop slot (= not only more space but lesser wages, higher map speed and lower supply requirements compared to two troop types).
So what would I change?
Cavalry:
-High agility/strength
-High power strike
-High riding
-High (200-250+) weapon profeciences
-Low/no Ironflesh
-Low/no Shield
-Low/no Athletics
EITHER equipped with ONLY a two handed weapon OR ONLY shield and lance. Or, in case of the councilmen for example, only a lance/spear is good as well. Or give them 1-hd weapons but no shield.
You would either have an offensive cavalry branch (without shield) or a defensive one (with shield). "Offensive" and "defensive" are just sub-classifications here, cavalry has to be HIGHLY offensive, with very little defensive capabilities. And, most important: without horse they have to be near useless. Especially the "defensive" line, with only having their lances to stab enemies in meele.
You could use the offensive cavalry branch for dealing highest damage on open fielded battle, and also for having top tier infantry on sieges which can deal huge damage, but in both scenarios they would be highly vulnerable to archers. Yes, the armor is good, but low (best would be 0) ironflesh and no shield equate this very easily, and you will definetely lose a lot of knights, if you use them as infantry during sieges or don't hide them from the enemy archers on the open field.
On the other hand you could use cavalry with shields, but they are only armed with lances/spears. On sieges they would last a bit longer than the offensive cavalry, but with their lances they would be pretty useless in meele. On open fielded battles they have bigger chances to reach an archer line they attack from the front, but they will also suffer losses due to no ironflesh (or being dismounted, which is effectively like a loss). So better hide your cavalry until the right moment comes.
Infantry:
Infantry has to become the backbone of your army, and this is easily balanced if you make them as tough as leather! This means on the first place:
Shields for top tier infantry!
All the top tier infantry at the current game doesn't have shields! Varangian/King's Berserker, Einherjars, Champions, Blademaster, (Elite) Halberdiers, Sergeants and so on never or seldom own shields. So you don't use them, because compared to their wages and the effort to train them chances are too great they don't even reach the enemy.
Elite Swordfighters, Highlanders, Huskarls and so on do have shields, but they are not good enough to establish a bridgehead on the top of the ladder, or even to slaughter some dismounted knights. Even with a 200-Huskarl army with 90% shields I only see my men being knocked out or dieing at the top of the ladder, like flies, without harming a single enemy!!!

. If I upgrade the Huskarls to King's Berserkers the losses become even worse, but among all these orange and red messages sometimes a green one pops out... at least...
So make infantry on first place incredibly tough, and on the second place let them deal a good amount of damage.
-High strength/agility
-High ironflesh
-High power strike
-High shield
-High athletics
-nothing meele-important low
-good (but not as good as the knight's) weapon profeciences
Good/best shields, good or even best weapons, good armour. (Not the best, this is reserved for the knights though)
Infantry would become enormously important:
- it would be the only troop type that can soak up enemy fire without heavy losses
- chances would be increased that an infantry block can stand a knight attack
- so you would be forced to send in your infantry next to your cavarly, because last one would be slaughtered after it has lost its attack momentum. Or you would have to send in your infantry first to break up enemy lines, and afterwards send your cavalry to clean up the rests. (= more realism)
- in sieges Infantry would become the only opportunity to reach the top of the walls
If you combine a block of 60% defensive top tier infantry, 20% old offensive infantry (Berserker, Champions etc.), and 20% spearmen (also with shields) your enemy would have something he can't make a dent in
This wouldn't only solve the problem of unbalanced sieges, but would also increase standard battle behaviour.