Toshiro takes the first round and that's about it. Kuwabara becomes to much for him after that. In CB, Kuwabara gets a rather huge upgrade in terms of stats and abilities. As posted by Yusuke52, he was able to keep with Hiei while they were chasing Sensui and Hiei was able beat a huge gas explosion to Yusuke that was less than meter away from him and escape it with Yusuke in hand (calced at mach 15-20). It's also worth noting that he should be superior to Younger Toguro who was fighting with Yusuke at mach 25 speeds which surpasses anything Bleach. His durability should also be beyond Toshiro's dc, given he was taking attacks from defense armor Sensui. Also his dimension cutting also ignores distance and conventional durability which makes Toshiro's flight and durability pointless. Kuwabara simply outclasses Toshiro and his hax give him to much of advantage.