spirits
I guess where it balances out in their mind is the fact that spirit offers active effects like Call lightning. Man that hits like a truck last year. But yea, someone already did the math and the banners give more support than spirits.
An infinitely shorter cool down may be a contributing factor as well. Spirits’ effective radius is also larger by 400. However, banners last longer, cant be killed and offer 5 active skills on top of their passive buff.
It is not what you do, but how and why you do it that counts.