There is no way to prove or disprove such claims. You have mentioned the Sarasvati hymn in Rig Veda VI.61. There is another mention of Sarasvati in Book 7.
This stream Sarasvati with fostering current comes forth, our sure
defence, our fort of iron, as on a car, the flood flows on, surpassing
in majesty and might all other waters;
Rig Veda VII.95.1
But in Rigveda 10:53:4, all varnas and nishadas are said to perform sacrifice.
It doesn't actually say that:
O ye Five Tribes, be pleased with mine oblation.
Some devata is the speaker of that verse, he offered an oblation, and is asking "the five tribes" to be pleased with his oblation. Nowhere is it saying that shudras, nishadhas, etc. are ...
"As for Purusha Suktam it's definitely a hymn to Lord Rudra".
So Let’s Start Analysis on the basis of Various Upanishad.
Let’s begin this Mysterious Secret with the Following Verse.:
सर्वयन्त्रसर्वतन्त्रसर्वपल्लवस्वरूपायेति ॐ नमः
“Sarva Mantra Sarva Yantra Sarva Tantra Sarva Pallava Svaruupaya Iti Om Namah Shivaya