Not sure how to call this one..
The thing is, Junzo easily countered Danny Rand's attacks, but only when he had the Iron Fist power, but I don't think the writer really understood how the Iron Fist chi works, and thought he was nearly powerless without Shou-Lao the Undying's chi. Danny has matched and defeated Steel Serpent when he had Shou-Lao's power....
And when he was "tired" from drawing on the chi, that's when Night Thrasher gave him problems...