That's an interesting point, actually. If we assume the attacking Wizard is in the Wish economy and has "unlimited" wands, then why not the Wizard who equipped the army? Give infinite amounts of equipment on both sides, and the the army has the advantage of more standard actions.Or just hand out rings of counterspells like candy; they're wish economy fodder after all. So are minor energy resistance rings, and Necklaces of adaptation, and rod of flame extinguishing, and every potion.
But then he's either:Fectin, blasted... range is based on caster level. That's why the wizard is flying - presumably his lessers are ground bound, and he can literally dictate the range of the encounter such that his higher caster level gives him impunity. Though, yes, if you put the wish economy in full swing with an army, everybody has access to one-use magic items of good caster levels. But the high-level caster can still take advantage of globe of invulnerability for a minute of immunity to these lesser magic items, while he blasts away (and it would be difficult to cover an entire army with globe of invulnerability). I think anti-air from swarms of low-levels would be a no-go.
A) Using his own spell slots.
B) Using items that are beyond the Wish economy.
Which means he's very limited. He has nowhere near enough juice to deal with a spread out army, and every time some jackass pops up a tower shield, it eats a precious slot or charge.
I don't think anybody's claiming that casters don't hold all the cards, but armies include casters, have casters supporting them, and are often commanded by casters. A lot of the "armies are obsolete" stuff seems to ignore that, which is a bit like saying "Armies are obsolete in the modern day, because pikes and chainmail don't do shit against a combat helicopter"