Agreed but I also think IB only worked because of Surbhi. Annika existed purely to highlight the dark and light parts of Shivaay. As a character she was very poorly written (probably the worst written character on the show; even the writers began to forget things about Annika after a while in the OU). But Surbhi brought her to life completely which is what a good actor brings to the table.
Conversely I am probably one of the very few who believe that Omkara was written the best out of all the characters at the beginning, and that suggests he was probably meant to be the main hero (eventually). But Kunal was never able to deliver Omkara like Nakuul was with the much more poorly written Shivaay; which is why the latter became the lead.
An actor's performance should be expected to overcome poor writing, especially in Indian soap operas where that is basically the way of life.