Good question.
Rcom has added advantage of 2G as well as 3G network. Only thing is that they should improve their service by providing better coverage. Which I believe they must be now concentrating on after closer of their CDMA Network.
No doubt CDMA Network of Reliance was very good and cheaper too.
So now they can offer cheaper data as 3G too. So the customer can choose either 4G/3G or 3G Only data option.
Having extra 2G and 3G tower apart from the 4G will also save them for network congestion as the load of users will be distributed.
Vodafone has quite good 2G as well as 3G coverage in Mumbai.
Further the most important thing is that if they implement VoLTE then they will have an upper edge over JIO.
At present Jio is on look out for new customers whereas Rcom already has enough subscribers which they can retain only if they take some serious and effective steps with regards to their 2G and 3G services.