>>106231871Airbending is OP as heck.
>Air is literally everywhere>They've got air superiority>They ride on large mammoth like creatures>They can suck the air out of your lungs>They're incredibly quick, nimble, and can dodge most your moves>They can extinguish flames by cutting off oxygen, threatening the firebenders most as they can't cut off their source of bending like with water and earth>they keep warm in frigid and mountainous terrain>Airbenders were the majority in the populationThey were lucky they were pacifists, so with a surprise attack under a power boost they were able to wipe them out.
Remember how Gyatso was standing amongst a pile of fire bender bodies? That was just one practiced airbender losing his temper, breaking his vow, and fighting back.
Plus they wanted to kill the Avatar before he or she becomes a problem.