I get you feel the way you feel for whatever reason. What I do not understand in your explanation is that it is the backstory of the MC being comforted by Alexis when he was younger. The MC did not recall that (and we did not learn that) until much later in the game.
Or maybe because Erynn's story isn't central in the first four chapters? Well, in that case, neither are the stories of Elena, Layla, Valeria, Gabi, Nikki, or Cara. Because we have not dived deep into the Erynn arc? That doesn't make sense either. The MC has carried a flame for Erynn from the beginning. They meet back up and she is even more beautiful. He eventually pulls his head out of his ass and realizes that Erynn was not the one who hurt him. His memories of what happened were completely false. Then he thinks Ethan is in the way in the present. Again, he pulls his head out and listens to Erynn's story.
The MC was in love with Erynn since he was younger. She was always "the one." How is it more difficult to follow that than to follow the Alexis story?
I guess it may be possible through player choices to skip parts of her story. You may have chosen to not help Erynn in the two cases where you were given the choice. I do not understand why people would choose that option (other than exploration) considering this is a story about Erynn and the MC. It is like watching Star Wars and skipping the Jedi content because you don't like Obi-Wan. Who does that?
I do not understand the people who are like, "Erynn? Meh."