So let me get this straight

[shelke]

I'm bashing kishi's logic. Kakashi should not be able to handle PS, or even be able to use it.

We are in agreement then, but apparently, Obito's honest ghost has possessed him. If that makes sense.

 

[kuro zetsu sama]

He also has the remaining chakra of the sage left in obito giving him more durability and we still dont know if he can handle it he just used the ability.

 

[NukaCola]

Kakashi has chakra of the sage
SO6P > Hashirama's DNA > Uchiha's

 

[DarkStar1]

Obito is a better genius apparently

 

[AlphaScythian]

The thing is that kakashi's body doesnt have to generate own chakra for susanoo.
Susanoo puts similar strain on body like gates.
User's cells produce more chakra thus it hurts in end. Eventually user improves at it and gets used to.
For comparison naruto didnt have to take baby steps nor mentioned any pain for BM avatar as he uses kurama's chakra mainly.

 

[SuperChief]

Obito's chakra and spirit is still fused with Kakashi. It's a temporary powerup.