The trinity is contained within scripture. It's a logical concept that can only be known and understood by usingthe rational mind. "Self evident" refers to axiomatic beliefs, which are not given in scripture. God gave nothing that is axiomatic(self evident), only what can be learned and understood from what He said.
"the putative leadership of the Holy Ghost of all believers is not there."
God does not dictate. His gift of free will was given unconditionally. He came here to teach and it is the same with the Holy Spirit. If one doesn't learn and understand, it does not mean the teachings weren't there, or were bad. He spoke only in parables for a reason. That was so that man would use His own mind. It was the same with Jesus.
Hub? God can be "understood?"
The ingredients to deduce the concept of the Holy Trinity are in the scripture, just like the Mariology is. It is not formulated in the scripture in the same direct way in which, for example, the Incarnation is formulated. You still need to engage your analytical and synthetical skills to form the concept, and as the first four centuries of Christianity especially show, you may get it wrong.
came here to teach and it is the same with the Holy Spirit.
Partly true, but do not then proclaim that every truth a Protestant community of faith holds up is inspired by it. However, the scripture teaches two things about it:
The teaching of the Holy Spirit is clear and unambiguous:
the Paraclete, the Holy Ghost, whom the Father will send in my name, he will teach you all things, and bring all things to your mind, whatsoever I shall have said to you. (John 14:26)The teaching of the Holy Spirit is is available sacramentally through the "unction" of confrimation (chrysmation):
let the unction, which you have received from him, abide in you. And you have no need that any man teach you; but as his unction teacheth you of all things, and is truth, and is no lie. And as it hath taught you, abide in him (1 John 2:27)