I think it would really come down to training. Given that unicorns are presented as being very highbrow and aristocratic, I'd think most of them would believe direct combat beneath them. I think the point stands that in most cases, unicorns would probably be at a relatively even field or possibly disadvantage against
E Ps or Pegasi. Sure, specific Twilight level unicorns could certainly whip up uberspells, but putting the entire weight of the army on them would be like trying to win a war with nothing but tanks. Yes, it's dangerous to go up against, but it's also limited in scope and will usually go down against a more versatile opponent.
Pegasi have the most pronounced combat advantage; any enemy without a ranged attack is kinda screwed, and they have weather control to boot. Here's how I'd boil down the races combat potential:
Unicorns:
Glass Cannon, all the way. They undoubtedly have several very powerful spellcasters who could probably cause enormous amounts of damage, and are, on an individual level, probably the most powerful ponies. The catch is that 1. Most unicorns aren't that strong, and telekinesis can only reach a level comparable to physical strength of the other races and 2. chances are that given the society we've been shown, most of them probably don't have much combat training. They'd have to rely very heavily on tactics and careful applications of what strong spells they have.
Pegasi:
Fragile Speedster. They'd be best served by keeping their distance and not doing direct combat. Lots of dropping crap on enemies, screwing with the weather, etc. If they get into hoof-to-hoof combat, they'd do better than unicorns but not as well as Earth Ponies. Their weather abilities give them a degree of versatility that the other races lack and overall I think they're probably strongest, especially given their militaristic culture.
Earth Ponies:
Might Glacier. Pretty much they have to turtle, but they're very good at it. Chances are they have much more food and resources than the other races, and I'm guessing that due to the physicality they'd do well in direct combat. The lack of ranged attacks is a problem, hence why their strategy would have to consist of attrition; hoard food and try to outlast the other groups.
edited 28th Oct '12 8:53:24 PM by JapaneseTeeth