If the Mormon/LDS church was false, wouldn't their missionary strategy have killed it by now?

Okay, this is funny to me because my boyfriend and I were talking about this earlier. One of my roommates has been meeting with the missionaries, and today my other roommate (an RM) and my boyfriend (also an RM) were talking about how they weren't really that good at teaching (after all, they're both only 20 years old or so) the lessons...but the Spirit is still there, despite their shortcomings.