Youyu was simply caught off guard, given that she had no experience facing fighters of the same rank, to say nothing of the fact that Zhang Xiaobo, who had entered his burst phase, was originally a whole major rank above Youyu.
Indeed, Zhang Xiaobo's strength during his burst phase ranged from the mid to the peak of the White Cloak period, where rank levels fluctuate somewhat, shifting with emotional changes and personal condition, but clearly, even at his minimum combat level, Zhang Xiaobo far exceeded Youyu by a major rank.
What exactly does a major rank represent? Anyone familiar with Mecha Battles would not find this strange, as the gap typically manifests amongst regular pilots.
In other words, if you're not even at the basic pilot level and can't meet the qualifying standards, it's the same principle as the gap between first-tier, second-tier, and third-tier experts in Galactic Warfare.
