An Amendments Convention has exactly the same authority as Congress with respect to proposing amendments, no more and no less. Article V states that amendments may only be proposed "to this Constitution" which implicitly forbids the abrogation of the current Constitution and the writing of a new one. Yes, an Amendments Convention could propose 80 amendments to the states for ratification that would reshape the Constitution, but, no, an Amendments Convention could not start all over again.
The decision to restrict an Amendments Convention to a single subject or to open it to all possible subjects is a decision for the states, and the states declare their desire in their petitions to Congress for a convention call. Each document has a different view as to enforcing this decision of the states, which is why the ALEC document should be read first, and then the ABA document as a rebuttal.
Roger that.