But she had incredible character development back then. Sure, she wasn't the strongest female but she actually had a personality other than screaming Meliodas-sama all the time.
Ever remember the time when she used to have a weak resolve for her people and an extreme lack of self-esteem and yet toughened up to protect that one kid who wasn't actually a kid? And then soon after she discovered that, she didn't break down in tears, but smirked over Ruin's failure to realize what she actually aimed for.
If it wasn't for her powers awakening, all of the people of Liones might have met certain doom against Hendrickson. You can't call that being a "background character since the beginning" when she was one of the most influential in the Liones battle, being the one responsible for turning the tides completely.
That and there were plenty tiny moments in the inbetween arcs where she showed she had an actual character. She was given the most attention among the others girls e.g Diane, Elaine, etc. I'm not going to argue about the current state of her character because it's basically non-existent now, except when she returned to being herself for one chapter, smirking over the fucking Clown King because he underestimated her power
But I guess most nowadays always need a Mary Sue like Erza to satisfy their hunger, because they can't look at a physically weak female without berating the poor girl. I'm sure glad Elizabeth turned out the way she was in the Holy Knights crises because she sure would have liked her enemies underestimating her so she would smirk over their stupid failures.