Dylan is perhaps the main, even the most main, he appears in the game probably more often than Sophia, who is named the main character before
Ellie is not the main character and never was, except in words, and she receives very little attention in the story. She has no own choices, nor does she have a leading role in events on her pov.
The Ellie/Dylan bonus storyline is lead from Dylan's point of view. In addition, in order to make Ellie another "the goal" for Dylan, her character was completely rewritten. No, Ellie doesn't look like the main character in this story.