Versatility is important in a singing competition, especially for a show like SRGMP. The ultimate goal of this competition is to give Bollywood a good playback singer. If you look at successful playback singers like Udit Narayan, Sonu Nigam, Shaan, Shreya Ghoshal, Sunidhi Chauhan and even KK - they are all quite versatile singers. Do they have one genre that they absolutely excel in? Yes, they do. But that also does not mean that they lack the ability to sing in other genres.
At this stage in the competition, when the singers are just discovering their true potential, it is not right for them to limit themselves to their comfort zone and present that to us week after week. It doesn't show their real ability or the scope of their talent if they sing in the same genre from auditions up to elimination.
Coming to Ranjeet's case, we all realize he is a good ghazal singer. If he continues to work hard, he will excel in that genre one day. But "one day" is the key term there. In order to get to that one day, he has to step out of his comfort zone and show us his true potential. Ranjeet has to attempt a Bollywood number ... if he does not attempt it we will all continue to assume he cannot sing mainstream Bollywood songs. And that may or may not be true.
When you're a participant in a reality show, you haven't earned the right to pick and choose which genre or style of song you would like to sing. You have to showcase your versatility and show all aspects of your singing. It is evident that flaws will come out when one steps outside the four walls of their little box, but it is how those flaws are improved as the weeks go by that gives one winner-like qualities.