She absolutely is an important part of the story, sorry but you are really making no sense here.
Important to the story? You could take every scene with her out and it would change nothing. She basically only interacts with MC and sometimes her sister and that is it. She has no impact on any other character.
It's not like the banner art needs to show the female character with the most screen time.
Do you know what false advertising is or clickbait?
I don't know if you've played these games but I'll use them as examples.
It is like putting Sofia on the banner of the game Melody instead of Melody herself.
It is like putting Jennifer on the banner of the DmD instead of D herself.
It is like putting MC's sister on the cover of Parental Love instead his actual family.
The Fing Maid should be on the banner! She seems to be the main character MC interacts with from what I can tell.
Honestly I skip over everything outside of the house and I'm just guessing based on the images I zip past.
This game is like 2 games mashed into one. 10% of the home life with the daughters and 90% of outside thug life. So why misrepresent what the game is about on the banner?
If anything the banner should be of the dozen other women MC has sex with!