Shyvana does a ton of damage even without the presence of any damage items, she simply needs to build tanky and take very little damage while dealing them. Shyvana can simply win early game by maxing her E, this will allow her to debuff the targets while dealing tons of damage despite the annoyance of the poke that goes through minions. After she uses Flame Breath on her enemies, they will most likely under estimate the debuff, combining with other abilities, she is able to take Janna's breath away with how fed and tanky she is.