De PFSRD - Arquétipos de Classe :
When an archetype includes multiple alternate class features, a character must take them all—often blocking the character from ever gaining certain standard class features, but replacing them with other options. All other class features of the base class that aren't mentioned among the alternate class features remain unchanged and are acquired normally when the character reaches the appropriate level, unless noted otherwise. A character who takes an alternate class feature does not count as having the class feature that was replaced for the purposes of meeting any requirements or prerequisites.
( ênfase meu)
Então, sim, você deve tomar ajuda defensiva. Não consigo falar com essa habilidade específica, mas, em muitos casos, os arquétipos intencionalmente dão um substituto mais fraco para um recurso, a fim de dar um substituto mais strong a outro recurso.