The vedic Hinduism started with no GOD at all. It all started that people started to believe there is a phenomena, some spirit out there which is controlling the events that are occurring in the universe/multiverse. That Cosmic soul they named it as GOD.
Dharmic philosophy includes both Natiks and Asthiks
Āstika and nāstika - Wikipedia, the free encyclopedia
i don't think you are right...During vedic times, although no names were assigned to god, they still refer to that unknown entity as "Truth" and that no one can deny its existence. Even in rig veda, they use terms like "One" or "Truth".
Then even nothingness was not, nor existence,
There was no air then, nor the heavens beyond it.
What covered it? Where was it? In whose keeping
Was there then cosmic water, in depths unfathomed?
Then there was neither death nor immortality
nor was there then the torch of night and day.
The One breathed windlessly and self-sustaining.
There was that
One then, and there was no other.
At first there was only darkness wrapped in darkness.
All this was only unillumined water.
That One which came to be, enclosed in nothing,
arose at last, born of the power of heat.
In the beginning desire descended on it -
that was the primal seed, born of the mind.
The sages who have searched their hearts with wisdom
know that which is is kin to that which is not.
And they have stretched their cord across the void,
and know what was above, and what below.
Seminal powers made fertile mighty forces.
Below was strength, and over it was impulse.
But, after all, who knows, and who can say
Whence it all came, and how creation happened?
the gods themselves are later than creation,
so who knows truly whence it has arisen?
Whence all creation had its origin,
he, whether he fashioned it or whether he did not,
he, who surveys it all from highest heaven,
he knows - or maybe even he does not know.
That "Truth"/"One" later become known as Brahman in vedanta and shared exact same traits, most important being that "One" cannot be described, only experienced.
So hinduism always had concept of "God" but its characteristics/personalities were debated among rishhis.
Also astik and nastik are much broader terms...not just limited to believer/non-believer.