I think he was just pulling a bait and switch, actually. Tatsuki was established as Ichigo's childhood friend who knew how to fight, and Orihime was that quirky girl with a crush on him. Stick them both in danger, and obviously the trained martial artist will-WHAT?! The untrained girl with no fighting skill saves the trained fighter who got her ass kicked using superpowers she manifested on the spot?! What a twist!
But seriously, Orihime always had enough of a focus placed on her that it was pretty clear Kubo intended to use her from the start. And while Tatsuki was established as "Ichigo's childhood friend," she was shown interaction-wise to be Orihime's friend, rarely interacting with Ichigo. Which apparently made her (alongside Chizuru) Orihime's equivalent of Keigo and Miziuro, thereby rendering her unimportant outside of comedy and high school drama.