Jman is in top ten in naruto world ! He has got everything a nin would want ( stamina , chakra, techniques, experience )
If raikage same level as KB so Jman is also comfortable kage lvl so ...
Remember Jman was the strongest ninja konoha had for a longtime so he is capable of beating KB . I love KB too but Jman here can beat him.
He can fight against full jinchuriki transformation on top of gamabunta .
His sage mode isn't complete but it never finishes so he can fight in sage mode during the entire battle !