A) A film's purpose is not to world build, it's to develop characters. You can have all the great world building you like, but if your characters and story are lacking then the world building was moot. See the Star Wars Prequels.
This is a ridiculous comment. Part of a film's purpose is absolutely to world build, I honestly don't know how to respond to this. Come on....
Not every character can be a main character.
B) Liz was absolutely Peter's LI in Homecoming, she's one of his primary motivators for doing things in the film. The end of the movie is him choosing not to dance with her at Homecoming and instead stopping her father and this is seen as a "hard" choice. She is his main love interest in the film, that really ca't be argued.
She was his love interest in that film yes, but the film clearly showed her as a character intersecting and moving through Peter's coming of age story.
Again, characters like this are perfectly fine and indeed required.
C) She has no agency. Her "being capable" is not agency. She exists to flirt with Peter, that's it. There's no plotline involving her escaping her abusive father and trying to make it as an actor in the big city while dating a affluent friend from school who has provided her with the first real kind of financial and emotional stability in her life but who she does not truly have the same feeling towards. Liz exists to serve Peter in Homecoming. MJ exists on her own in Raimi.
She had enough agency on show for a side-character, she is shown as able, determined, interested. She was head of the group preparing the Homecoming dance, leader of the Decathlon team, someone who would call Peter on his shit due to her principles, etc...
If you're going to hold up Liz and Rami's MJ and compare them without context, sure, otherwise no.
she was not intended to be as much of a focus as MJ from Rami's films. MJ in Rami spanned all 3 movies, Liz is a side-character in the first MCU SM. Obviously MJ was more fleshed out, that doesn't mean Liz was a poor side-character.
Liz didn't have agency because you only see her when Peter is around. You don't follow her, and her story is dependent on Peter. That's not agency. What does Liz do on screen that shows she has agency? Throws a party where the story centers it around Peter showing up to prove he knows Spider-Man? She is a capable team lead who leans on Peter to win? Does a late night swim at the pool to invite Peter to participate because HE needs to have fun? Tells Peter at the end that he should figure out his shit? She is designed to prop Peter up.
MJ was cute and said lines that resonated with the audience. It isn't fine because then the message of the story weaves through one character, and that makes side characters purely story pushers.
There is a reason why SM1 and 2 are valued so much because Raimi knew side characters need to embody the message he was telling just like Spider-Man. They all had to give up what they wanted the most.
Her only being seen when Peter is around doest mean she didn't have agency. She was not a main-character, and that's actually okay.
Agency reasoned above.