Korra and Asami perfectly complement one another, their opposite personalities and abilities perfectly complement one another.
Korra is a very powerful bender, Avatar, master of all four elements and spiritual, while Asami is a very skilled non-bender, a genius with exceptional knowledge and skills regarding technology and science, and not spiritual.
When they fight together, they are in perfect sync. When they are together no one can stop them, no one has any chance against them.
They are the most powerful couple in the world.