Onnamaou-sama wa Yuusha-kun o Taosenai. - Ch. 21

[Juggernautbob]

Maou successfully sabotaged the hero.... (?)

Indeed. She accidentally prevented him from getting his power-up.

I'm not so sure about that, I feel like the Sage was lying about the spring powering him up, and the real reason for his trip there was so that he would learn to fight even when he's scared.