Archer needed to focus, really. They needed to separate the boss from the chaff and that was something he could do, with or without power. He'd have to apologize to Rin for using so much power from her but...

"I am the bone of my sword
Steel is my body and fire is my blood
I have created over a thousand blades
Unknown to Death, Nor known to Life"

Nanoha may be unfamiliar with the spell words but he was certainly powering up for something big. He just needed a little more time. He took what spare focus he had to create six swords, firing them at the boss. They weren't doing any good but it did keep the boss creature focused on the pain rather than trying to kill them.