Well when you look at their capabilities, they both seem extremely powerful, but there are several ways to get around their abilities.

Kururai mainly uses his speed to get around, but Koguja has clairvoyance. Kururai follows the laws of physics (for the most part) and has a hard time being able to see where he's going. He must predict where to stop, etc.. Also, in the RP, you can be extremely powerful, but the moderators on it limit how powerful you can be. For example, there is one person who can copy other's abilities, and turns into glass right before dying :/ Kururai actually obtained a lot of those stronger abilities throughout playing the RP, eventually learning things.

Koguja's name means Collector, which hints at his multiple weapons with sealing capabilities. He essentially collects weapons with the ability to seal another's ability. The fairest I can see the battle happening is: Koguja uses his Zanpakuto and seals Kururai's speed. He uses another sword and seals Kururai's aether control. After, Koguja seals Kururai's instant heal. All Kururai has left is Dragon shouts, luck, teleportation, and a vast amount of weapons (and of course, basic things that come with his weapons, like Kido (Zanpakuto) and Keyblade Magic (Keyblade)) Koguja still has spell casting, dragon shouts, arrancar/SOLDIER physique, and clairvoyance (basic other stuff such as Keyblade Magic and Kido)