This is pretty much it he cant use his can't-hit-me-no jutsu in that dimension as that is where he sends his body parts to avoid damage. Thus he is grounded to his base abilties there which puts him on even footing with Kakashi.
Originally Posted by Kenny Bones
Tobi utilized the Rinnegans 6 paths with Edo former Jinchuuriki + Bijuu power to take on KB, Naruto , Kakashi & Gai that's a lot of power.
Obito is on the same level as Kakashi with aslight boost because he has Zetsu/Hashrima power thus can spam his MS.