User blog comment:Kurare/Undervalued characters/@comment-24165551-20140919174451

Aizen didn't actually think Orihime was important, he used her as bait to draw Ichigo & co and half of the captains into Hueco Mundo. Yamamoto only thought she was important because he thought Aizen needed her for his plan. Ironically, he was right, but only because he failed to see through Aizen's ruse.

Orihime is hardly underused in the series. She's not much of a fighter, but there's two reasons for that:

A) Despite her abilities, she's still has a frail human body that could not withstand combat with entities like Shinigami, Hollows, or Qunicies. The other human protagonists aren't normal humans: Sado is a fullbringer, Uryu is a qunicy and Ichigo is an Ichigo.

B) Orihime is too nice. She's completely non aggressive and has zero killer instinct.  That's not a put down - most people in real life are like that.  Remember, the captains, sternritter, and even the arrancar were/are all part of a military.  Uryu and Ichigo both trained to fight, and Ichigo has a learn uberfast plotkai ability.  Only Sado also has no real training, but he's a stereotypical Tough Guy.