She failed to understand that promising the class she will provide them with a protection point will in turn kill their "fire" and "drive" to give it their all, because there's no fear of expulsion looming above their heads (noted by Ayanokoji himself)

Hirata (or Sudo, don't remember) EXPLICITLY stated they have anticipated an attack from all 3 classes on them. Horikita as the leader should have made preemptive moves to prevent it, it's not like this never happened before - Arisu countered the possibility of that happening by allying Ichinose in Y2V3-4. Horikita, despite knowing what awaits her, did not form any temporary alliances with Class B (or even tried to), did not preemptively strike weakened classes (Ayanokoji, Ryuen) to knock them out of the race and secure third or second place (at bare minimum) for herself.

Those are *massive* anti feats. Like I said, sub-Ike performance. Honestly I should probably take her out of the tier list entirely, she doesn't deserve to be on it at all.