This idea of rAmAyaNa representing the transit of the migrant Aryans from North India to South India, seems to be the brain-child of Ralph T.H. Griffith, one of the early translators of rAmAyaNa into English.
Considering the transport infrastructure available in the Deccan Plateau of those days and the impenetrable forests, mountains and rivers dominating the terrain, it was most unlikely that rAmA-lakshmaNa and Sita, could without horses or carts have traversed the country from North to South. Besides, for rAmA, there was no such compelling circumstances.
Compulsions might have arisen subsequently to Aryans to flee to South India when there were further invasions from the Northwest by more Indo-European-Iranian-Semitic-Mongol colonisers. Theoretically, there could have been no end for this fleeing from North India to South India, because invasions took place up-to 1800 a.d. The invasions became stronger and stronger with the invention of fire weapons like guns and mortars. The Aryans who depended more on imaginary chants (mantras, astras and tantras) could not resist the Turks, Mongols (Moghuls?), later Iranians and the Europeans and the southward emigration became inevitable.
Both rAma and rAvaNa were Aryans. The fight among them was for a lady and probably hegemony on some territories. It has nothing to do Aryan-draviDian or Aryan-buddhist battles or squirmishes.