User blog comment:Xilinoc/Ch. 571 (Yachiru's gonna wreck it)/@comment-8669536-20140305144023/@comment-8669536-20140306111822

Indeed she is probably strong, but saying she is at the level of a captain is just too much. She is lieutenant-level, maybe very strong lieutenant level, but still not captain-level. And it has been shown that a lieutenant-level fighter with Shikai can't defeat a Sternritter.

1. Ichigo wasn't very strong at the time, and besides, Yachiru has had all the time in the world to get accustomed to his Reiatsu. Maybe she has become stronger by it, but I don't think she can become that strong by simply being close to a powerful Reiatsu.

2. Speed doesn't necessarily imply great power, just that she has great speed, which may aid her in her fight, but it is probably not enough to efeat a Sternritter. Besides, Ichigo was weakened at the moment by Kenapchi's vast Reiatsu and even if he hadn't been he wasn't exactly fast in the beginning of the Soul Society Arc.

3. So, Yachiru used her lieutenant-level Reiatsu to frighten a Shinigami who was neither captain or lieutenant. We don't know how strong he was, he could have been at the power level of an unseated officer for all we know.

4. Yes, she's strong. And that might impliy that she have high amounts of Reiryoku, however, it doesn't show that she's captain-level.

5. That she's confident in her abilities doesn't necessarily imply that she actually is strong. You know who else was confident in his abilities? Why there's a very long list of people who have been confident in their abilities to defeat lieutenants and even captains, or maybe even lower than lieutenant. Abirama Redder, Edrad Liones, Renji Abarai (when he fought Ichigo for the second time and later on Byakuya), Findorr Calius, Yumichika Ayasegawa (versus Ganju), Izuru Kira (versus Matsumoto) and so the list goes on... And I know that several of these won only because of their unique Powers, but in Bleach these have to be taken into account when you calculate someone's strength.

My opinion is, and I might be wrong, that Yachiru is a lieutenant-level fighter, and an exceptionally strong one, but she's not captain-level. And to be captain-level, or at least be in possession of a Bankai, is needed to defeat a Sternritter, and Yachiru is neither.