Its not really that Madara and Obito aren't powerful. One on one, both of them could probably take out the vast majority of the shinobi in the series without breaking a sweat. They don't seem to be on the same page in terms of their overall motives and battle strategies.
Madara doesn't seem to be trying very hard. Just like when he fought the Kage, he seems more interested in playing with his opponents than he is at beating them. This means that Obito is pretty much on his own in combat. Madara seems content to just absorb attacks and regenerate as needed.
Obito was on the offensive until the Juubi was revived, and then wanted to immediately complete the technique. Obito can't afford to take too much damage since he's not invincible like Madara, and likely wants to finish the battle as quickly as possible. It doesn't really help that Kakashi is probably the one shinobi in the world that can counter Obito's intangibility. If you look at all of Obito's previous battles, his victories were reliant on his intangibility. And the three times before when Obito's intangibility was compromised, he took serious damage. Minato countered Obito and hit him in the back with a Rasengan, Konan would have killed him with paper bombs if it weren't for Izanagi, and Torune infected his arm with insects when he was abducted.
are you serious??
