Had robotic forces already failed against the Flood?

Had the Forerunners already tried robots and Sentinel swarms against the Flood?

Their failure is acknowledged, while the proposed alternative favors simpler, effective machines.

A viewer objects that robotic forces had already failed in the setting, and a later comment names Sentinel swarms in enormous numbers. That outcome is accepted. The remaining criticism favors practical machines over technological sophistication. No successful replacement for the Halo Array is established by this disagreement.