Curate, connect, and discover
Marinette is the ideal that the audience is supposed to strive for. She has a loving family she spends time with, friends she cares about and who care about her, a hobby that let's her be artistic, a passion for said hobby that she hopes to make a career, high grades, participation in school as class president, and she serves her community by being a literal superhero.
Yes she has flaws, but by and large I'd argue that Marinette is THE girl the audience wants to be more like (with the assumption that all those positive things lead to a positive life)
Adrien is not only her foil, but he also teaches the audience a lesson. He is what the audience "thinks" they should strive towards. He is wealthy, famous, can speak multiple languages, does tons of extra curricular activities, is top of his class, and he comes from a powerful family
But he is absolutely miserable
He teaches the audience that while perusing those positive things is good, they shouldn't neglect everything else like friends, family, and your own interests (even though that's not his fault). I'd argue he's where the audience is right now, unsure what they want to do, maybe not having many friends, perhaps stuck in a situation they don't like, and dealing with some baggage. Thankfully he has Marinette and the rest of the cast to support him. He learns to draw closer to others who care about him and learns just how little wealth or fame or any of that stuff actually empower him to live the life he wants to
TLDR: Marinette is THE role model and Adrien is the stand in for the audience. They compliment each other perfectly and I wouldn't have it any other way