First of all. Its not about popularity here.
Ishqbaaaz is not a love story in the first place. Its about the story of three brothers first and then their love stories.
Vrushika comparision with Surbhi is illogical. Both are popular in their own way. Vrushika got popular through D3 and Surbhi through Ishqbaaaz.
Gul is taking their love stories in a sequential manner. First ShivIka, Then Om's lovestory and then RuMya.
You may ask, RuMya has started before Om's. I wouls say the writers have so much messed up Ishaana's character tht they dnt know how to take it ahead.