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.
As Minato said, Tobi is someone who can only be defeated by someone with a very special skill set. Obito has a very rare ability with Kamui and also a very unusual body. This combination of abilities made him untouchable to almost every opponent he faced. Looking back Obito's rare abilities are really the main reason he was able to defeat powerful opponents. Also, Obito rarely fought powerful people before, he would simply avoid being attacked. We saw several times Obito was at risk of being defeated, against Minato, Konan, and even Danzo's guards he suffered significant damage.
When he first started fighting Naruto, Gui, and Kakashi, they still didn't understand his abilties, so they still couldn't touch him. Once Kakashi discovered how Obito's abilities worked he was able to use his own special abilities to neutralize or limit Obito's ability to avoid damage. Then there is the issue of Obito's psychological state, in the past Obito was in total control of his actions, he was thinking clearly and intelligently. After Obito's mask broke and his past was revealed, he stared to have a mental breakdown, he stopped fighting smart and became reckless.
Kakashi is the perfect person to fight Obito because he can counter his genjutsu, he can counter Kamui, he knows Obito, and most importantly he is able to get under Obito's skin because of their past relationship. One of the great things about Naruto as a series is that battles aren't all about raw power. Obito didn't win in the past because he was the most powerful, he won because he had a very special skill set and because he was very cunning. Obito also managed to hide his weaknesses by hiding his identity and hiding the origins of his powers. Once Obito was exposed he lost a lot of the advantages that had made him seem invincible.