Sorry about Mahavira. He is merely the last and most famous of Jain thirthankaras.
You fail to grasp my point again. Gods like Shiva, Vishnu, Ganesha etc represent the evolutionary chain of Hinduism. One that began with the Vedas and worship of elemental Gods like Indra, Agni, Vayu, Savitr etc.
Hinduism as a movement is defined by it's canonical texts namely the Vedas, upanishads, Puranas etc. SaiBaba considers himself an avatar of an earlier saint. The earlier Shirdi Sai Baba preached the Bhagavat gita(a part of Hinduism). Trace back every aspect of our devotion in today's Hinduism and you'll find they link back to texts like the Puranas, Upanishads and Vedas. That's how they're all part of Hinduism. The puranas and upanishads themselves evolved from the ideas espoused in the Vedas. Get it now? It's in this context that I say that since nothing that Hindus observed earlier/observe now has been traced back to something that was seen only in IVC, it's influence on Hinduism is nil/miniscule. Since the RgVeda sits squarely at the top of this chain, one has to conclude they were the first texts that led to Hinduism(again, they were orally conveyed for a long long time. Hence, one can't argue that texts older to them may have been part of Hinduism. If such a text existed, it would have been orally conveyed too.)
Wherever a sect has begged to differ with Hindu texts substantially, they have been considered as separate religious/philosophical movements. That's why Jainism, Buddhism and Sikhism are seen as different religions inspired by Hinduism. If a sect has chosen to reaffirm it's links with Hindu canonical texts, it has been retained as a Hindu sect.