If one studies, not merely reads, the Veda, one will know that there is no specific school of thought or ‘ism’
One will find worship of nature in its Glory, starting from Water,(Mantra Pushpam),Fire (Agni Suktham,Rige Veda),Earth(Bhoomi Suktham)
On Time, Rathri Suktham,Kala Suktham,Ushas Suktham,
On individual forces of nature, Surya Suktham,
On Values, Samanasasya Suktham.
On the world and on Monotheistic approach,
There is no specific system of worship or specific God promote as it were.
Hinduism is not founded by any one.
Vedas express Truth as experienced by the Rishis and the Manta grasped by them from the Ether.
As Lord Krishna puts it in the Bhagavad Gita, Reality or God reveals itself according to the disposition of the worshiper.
Reality however remains One,.
So on a cursory reading of the Vedas might give the impression that there are many Gods in mentioned in the Vedas.
As experiencing Godhead is intimately personal, Vedas knew that thee is no Universal Solution to the seeker.
One realizes God hood by His self enquiry and this depends on his tendencies or Vasanas,
So, much like a Super market, Vedas contain what ever that has been grasped for selection by the Individual.
That is the reason why do not promote one God.
Then why is it in the Veda Mantras on finds that Vishnu is the first God, in NarayanaSuktham, Vishnu Suktham, Shiva in Sri Rudram, Lakshmi in Sree
Suktham and Durga in Durga Suktham?
In philosophy it is called ‘Henotheiism’- the practice of praising one God to the exclusion of the others.
This has a Psychological element built into it,
You will not agree that what you do or follow is not the best among the available.
This reinforces faith and helps you spiritually.
Similarly there is no specific leaning towards Advaita,Visishtadvaita or Dwaita as such in the Vedas.
This is has come into being only after the commentators and the three Great Acharyas, Sankaracharya, Ramanuja and Madhwa,
They did not say anything new or what is not said in the Vedas.
Each interpreted the Mahavakyas of the Vedas from their stand point.
And they found supporting arguments for their approach from the Vedas.
Vedas , being an Ocean, it would provide you source for your approach.
Therein lies its greatness,
One more point one must bear in mind the time when these Achayas founded their Doctrines.
Sankararacharaya came after Buddha, whose Buddhism promoted Nihilism or Sunya Vada.
It is not practical to restore the Vedas with so many Gods as it were,for one without understanding, to have faith in the Vedas.
From one Sankara said not Two Advaita, it is easy for one who had been saying that there is nothing to believe that there not two, Advaita
Then came Ramanuja who established Qualified Non Dualism,not Dualism, Visishta Adavaita.
Then Madhwa came along and founded Dwaita, Dualism.
In essence there is no difference as far as the origin of these systems go.
The difference lies in interpretations.
Anticipating some bigots of Hinduism , there are slokas of Shiva by Vishnu and By Shiv of Vishnu.
Read my post on these.
Only those who do not understand the Vedas and Indian Philosophy would promote either Shaivisma or Vaishnavism.
Ekam Sat, Vipra Bahuta Vadanti’
The Truth is One,.
The learned, Vipra(this is actually a dig at the so-called Scholars, Krishna uses this term and Pandita in the same sense in the Bhagavad Gita)
Say It is many.