According to the show bible, which admittedly the show left somewhere in the first season … the population wasn't evenly divided amongst the tribes … numbers weren't stated but to keep the image an allure right, it would have to something akin to:
4/5ths earth,
2/3rds of what remains are pegasus,
and the last are unicorns… less than 7% of the populace. Of course, they also congregate with their own kind, so Canterlot is lousy with them but nobody else would really see them.
that makes Lyra's question in >>306698 a more interesting one.
…if they actually are 1/3rd of the populace, than I imagine the unicorns would be separated by distance-magic … those that can cause effects more than four body lengths away would be put in artillery, and the rest would slum with the cannon fodder, hopefully to learn good shield spells.
The pegasi's thing would be speed. If you can drop out of the sky (and what ground-bound remembers to look up?) from your enemy's blind spot, and stab them then fly back out of range of their anti-air attacks, you've displayed an advantage.
>>306689
>[Citation needed]
That's in general how it works here … emotional strength often comes hand in hand with physical strength. Once you learn you can lift, you believe you can stand. The chronically ill or weak-of-frame learn early about their mortality, and make sure they have a wider margin of error than what the natural born tanks exhibit.