Darklone:
You're thinking out of context. The battlefield is chaotic, and the archers would not simply be able to happily shoot down the magi. They may be distracted, by say a frontal assault, enemy archer fire or the like. Shield Brooch is difficult to answer, granted, but that can be dispelled by one of the higher-level opposing wizards.
Catapults are siege engines, not field artillery. Effective field artillery did not really appear until the 17th century at the Battle of Vienna when the Austrians turned back a Turkish army. Siege engines were almost useless against a mobile foe, and even if hit could only kill one or two. And the morale effect of being hit by a rock is not as shaking as a strange man in a long robe chanting some words, waving his arms and *wham* half your buddies are toast.
Regarding skirmishers: Ok, so they run. But then call in the cavalry and a withdrawal turns into a rout, which turns in a bloodbath. If they reform formation, they get fireballed.
Taren Nighteyes:
1. Granted, but orders to dispatch wounded enemies circumvent this problem.
2. Perhaps, but not strictly. Bardic propaganda and satire can be equally as effective. Read the virtuoso greater calumny effect. And of course the wizards are likely to have better economic admin, and hence better living standards- more loyal populace? Most people are materialistic, not ideological.
3. Moot point. The number of actual clerics on the field, as has been discussed, is likely to be insignificant compared with the number of grunts, which their fighting prowess is inferior to.
4. Arguable. Whatever happened to Intelligent (wizards) and Charismatic (bards/sorcerors). Powerful speeches by high-level bards or sorcerors written by genius-level speechwriters may give better interpersonal leadership, and strategic planning is likely to be better on the side of the wizards: higher Int and fewer moral restrictions.
5. Again, moot point. Intelligence can be long-term as well, and individual battles turn wars more often than not, particularly in medieval/fantasy settings.
Mustrum_Ridcully: Aura of courage is fine, but historically even crack troops would run before they suffered more than about one-third casualties, even from ordinary weapons. Conscripts would often run simply if charged. Seeing colleagues decimated in a fireball and not even understanding a) what's going on or b) just how powerful the enemy wizards are is going to shatter the morale of even hardened troops, paladin or no.
Tactics- is indeed a knowlege skill. Knowledge (War) from S&F
Wizards are 'hero' class, but only a few regiments of around 50 are required to turn the battle. The magic missile argument is a good one, but realistically, how many wizards do NOT take MM? A large magocracy could probably churn out around 20 such regiments. And of course the theocrats ignore such arguments with relation to the supposed hordes of clerics and paladins...