They both were like Oil & Water, from beggining itself. Before Indian also, Kamal was voicing strongly in support of IR, from the time Gentleman made ARR Popular. (Yes, roja & puthiyamugam only brought fans to ARR, its only Gentleman which brought producers in quee)
It shud be mostly that ARR composing for Indian and Thenaali wud be mostly director's choice, than kamal's. Like Harris composong for VV.