In the Sixth of the 13 ikrim, we say that we believe completely that all of the words of the neveim are true. In the 7th of the 13 ikrim, we say we believe completely that the nevuah of Moshe rabeinu A"H was true, and that he is the father of the neveim to those who came before him and to those who came after him.
Q: Why do we need to say the first part of the 7th one, "we believe completely that the nevuah of Moshe rabeinu A"H was true," when we just mentioned that we completely believe that all of the words of the neveim are true? Isn't Moshe rabeinu included in neveim?
A: One of the meforshim on the 13 ikrim gives an explanation that answers this question. He states that we know that the nevuah of Moshe was different from the nevuah of the other neveim in a couple of different ways. Firstly, Moshe's nevuah was peh el peh while the nevuah of the other neveim was in a dream. Secondly, the other neveim performed different signs to prove that the nevuah that they had was true, while Moshe didn't need to prove anything with nisim. Knowing this, we can understand why we needed to repeat that you should believe in the nevuah of Moshe. The 7th of the ikrim is coming to tell us that even if one of the other neveim comes and uses nisim to prove that his nevuah is true, if that nevuah contradicts a nevuah of Moshe, we believe the nevuah of Moshe even though he didn't use nisim to prove his nevuah to be true.
Also, based on the first part of what you wrote, not having to jump to the second part, maybe we wld say that even though he didn't "prove his points we still believe their legitimacy?