Avirah, missionaries do not do well with Tanach at all. Missionaries quote mistranslated and misconstrued verses, never in context. The vast majority, if any, missionaries, do not know Tanach at all. They are taught misconstrued and mistranslated verses that were taken out of context to “prove that their religion is true”. When you show them the context and the real translation they are always shocked.
As for the frei people, well yes, certainly we need both Torah Shebaschsav and Torah Shebaal Pe to be able to be a frum Yid, but that doesn’t take away from the fact that Torah Shebachsav is the foundation of Torah Shebaal Pe.