An article 5 Convention can not change one jot or tittle in the Constitution. It can only propose amendments. They must still be ratified by a 3/4ths majority of States.
All of this "runaway convention" rhetoric is used to scare the uninformed. READ the US Constitution, it is very clear. Amendments were made deliberately hard to get passed. This keeps us from passing laws on emotional knee-jerk reactions to some tragedy, real or imagined.
Yes, 3/4 of the states must still ratify. I would just say this. There are two methods of creating an amendment, Congress and Convention, basically. None of the 27 amendments began with a convention.
So, in that regard, an Article V convention is not a cut and dried easy-peasy process, IMO.