Along with Stefan. I see this take often that the main character was Stefan. I know Julie Plec said this after Nina left. I have to disagree with this take. Vehemently disagree. The first season was written from both of their perspectives, even the first episode starts with both of their diaries. A show can have two main protagonists and from season 1 to 5 that was Stefan and Elena.
Now 6 and beyond I have not rewatched yet so I cannot speak on that but I can say for certain Elena was one of the most central character of this show especially before those seasons.
Yes the story of Damon and Stefan relationship was a central plot to the story but so was Elena's relationship with them. She was decentralized for obvious reasons after Nina left but I think saying that Elena wasn't the main character and her relationship and arcs were less central to plot than that of Stefan and Damon's is disingenuous and diminishes Nina's involvement and impact.
I also think Nina deserved so much more than what she got in pay. I can't believe she was paid so much less than the 2 male leads.