hi Rock n roll I am loving your debate but must say just like RD B in North Indian music it was Ilaya Raja and NOT ARR who brought western music into Tamil music, here read on from wiki:
Impact and musical style
Ilaiyaraaja was one of the early Indian film composers to use Western classical music harmonies and string arrangements in Indian film music.[22] This allowed him to craft a rich tapestry of sounds for films, and his themes[23] and background score gained notice and appreciation amongst Indian film audiences.[24] The range of expressive possibilities in Indian film music was broadened by Ilaiyaraaja's methodical approach to arranging, recording technique, and his drawing of ideas from a diversity of musical styles.[22]
According to musicologist P. Greene, Ilaiyaraaja's "deep understanding of so many different styles of music allowed him to create syncretic pieces of music combining very different musical idioms in unified, coherent musical statements".[3] Ilaiyaraaja has composed Indian film songs that amalgamated elements of genres such as pop,[25] acoustic guitar-propelled Western folk,[26] jazz,[27] rock and roll, dance music (e.g., disco),[28] psychedelia,[29] funk,[30] doo-wop,[31] march,[32] bossa nova,[33] flamenco,[34] pathos,[35] Tamil folk/traditional,[36] Afro-tribal,[37] and Indian classical.[38]
By virtue of this variety and his interfusion of Western, Indian folk and Carnatic elements, Ilaiyaraaja's compositions appeal to the Indian rural dweller for its rhythmic folk qualities, the Indian classical music enthusiast for the employment of Carnatic ragams,[39] and the urbanite for its modern, Western-music sound.[40]
Although Ilaiyaraaja uses a range of complex compositional techniques, he often sketches out the basic melodic ideas for films in a very spontaneous fashion.[7][3] The Indian filmmaker Mani Ratnam illustrates:
"Ilayaraja (sic) would look at the [film] scene once, and immediately start giving notes to his assistants, as a bunch of musicians, hovering around him, would collect the notes [(musical parts)] for their instrument[s] and go to their places... A [film] director can be taken by surprise at the speed of events."[41]