In our culture, mythology and history are interwoven. Separating them is as easy as decoding information from DNA.
Earlier, historians predicted a friction between outsider Aryans and native Dravidas with the narratives in Vedas. But as the understandings got better we realised, the war between Asura and Devas mentioned in Vedas were not referring to Dravidas at all. Does this mean, there were no fights between the people residing on the north and south side of Vindhyas? The first acknowledged war between North and South of India was with Harshavardhana and Pulakeshi in 6th century AD. Does that mean, there were no wars before?
Epic Ramayana is considered to be the fight between Aryans and Dravidas. Periyar famously picked Ravana as a Dravida and asked his followers to worship Ravana over Rama. But his theory had several flaws. How come Rama, a dark skinned warrior became Aryan and Ravana a Brahmin king became a Dravida? End of the day, Ravana was not a popular character in south, so was not picked up for worship by people, in spite of enthusiasm by Periyar. (To be fair, even Ram Temples are not that many in South India. In fact, Hanuman beats Rama in popularity. The proverb in my native language says, "there can't be a village without a temple for Hanuman" - something which is not spoken about lord Ram). May be, Hanuman's character got appended to Ramanyana due to his popularity down South. Well , Ramayana could be a one shot epic or could have been getting appended over time. One can argue either way. The versions of Jain Ramayana (4th century BC) does not mention anything about the monkey kingdom or Ravana, which are present in the Valmiki version that we read today.
If I ask, who was the most righteous and powerful person in Ramayana and if you want to answer Rama, please hold on. It is true that Rama did win over mighty Ravana with the help of Ravana's brother. But there was another character in Ramayana who had defeated Ravana many a times at ease. He had the special power to grasp half the power of his opponent. Just like Rama, his wife was also taken away from him. His own brother had blocked his entry to his kingdom and got married to his wife. But unlike Rama, he punished only his brother. He threw him out to forest, got remarried to his wife, without questioning her chastity. It is strange that Rama makes a deal with Sugreeva, Vali's brother instead of Vali. Add to that, he also kills Vali in an unfair way, by shooting from his back (Vali does question Rama before his death. Rama replies, he could not have defeated him by right means).
Similarly, if I think of any other mythological characters which are very popular in South, first name coming to anyone's mind is "Bali". The Deepavali celebrations (Bali Paadya) in South Indian states, Onam in Kerala - all speak about the same story. A righteous powerful king, loved by his people who was sent unfairly by Vishnu to another world. He comes to visit his people once a year. Vali and Bali - do these characters have any other connection other than these were South Indian characters who were defeated/cheated by an Avatar of lord Vishnu? Or did these two characters evolve from the same but branched out later during Puranic period?
One of the stone inscription on the disputed site to Ram Mandir / Babri Masjid site in Ayodhya reads; the temple is dedicated to Vishnu, slayer of Bali and Ravan. Here, Bali do gets as much importance as Ravan.
With these in background, I reconsider the story behind Deepavali. For North India, it is about victory of lord Ram. For South India, it is Bali Paadya; remembrance of a righteous popular king who was defeated and sent to another world in an unfair way. Can Deepavali be the celebration of the same event, seen from two different prospective?