In SAC page it is clearly mentioned - "GSAT-18 satellite will serve as a replacement for providing continuity of Fixed Satellite Services (FSS) in Normal C, Upper Extended C and Ku-bands of INSAT-3C & INSAT-4CR". What i know is that INSAT-3C already has 24 c-band TPs & among them only 2 are allocated to broadcasting purposes, so GSAT-18 will not augment any capacity at 74° east orbital location.