IR no need to prove anything
Ilayaraja in his grand music era, has touched all aspects of music.
If you took ARR, He has created lot of music, but are they as varied as IR's? He never gave a Classical Music Like Salagai Oli, He never given a village movie like Karagatakaran and he havent given a Idhayam or Mouna Ragam like BGM. Why Arr can look at IR and immitate him in bringing the songs like IR did?
There is a case in this one and that is, IR if he compose songs like ARR then people wont say IR has composed this song in a great manner or IR has composed this for the youth, but they say IR is immitating ARR to match him which he dont like and as a senior he dont like his name termed in such a way and so he didnt like to come out of that path. and same applies to ARR, where if he compose a song for a village subject like that of karagatagaran then people talk about him as a person who get some improvisation from IR and that is why ARR has created a style and he dont like to come out of that.
So your point of IRR dethrone Arr is not at all possible for IRR has achieved such a huge feet he never wants to immitate a young musician inorder to get a name.
I hope my answer will satisfy your quest?