In regards to the posters who keep saying Zendaya's character is only 15 and shouldn't be glammed up like a model, I agree. No one here is saying she should be.
But that doesn't mean she has to look so dressed down and frumpy and unfashionable as Michelle.
Look at Liz and Betty/Gwetty in this film. Both girls are portrayed as cute/pretty/attractive and they both dress fashionable or "normal" ( with Liz probably being more fashionable than Betty ). Neither girl is glammed up to look like a sexy super model which would be inappropriate for their character's age. And yet, neither girl is deliberately dressed down to look frumpy, unfashionable, and plain.
If Michelle is indeed supposed to be Mary Jane Watson, a character who is in part defined by her beauty and attractiveness, all we are asking is why couldn't her character look more like Liz and Betty. No one is asking her to be glammed up like a sex object. But why go to such an opposite extreme to make her look so frumpy and plain ( which is counter to the character )?
if they wanted a more dressed down, "conservative" look for her, which would fit more the brainy/nerdy Ultimate MJ, then why not simply go for a look like these pics?
In these pics, she doesn't look as glammed up as "hot" Zendaya looks. She looks more studious, a bit nerdier, but she's still pretty and attractive. She's not some frumpy, unfashionable, plain looking girl like Michelle looks. And if she takes her glasses off, lets her hair down and styles it, and wears a nice dress to Homecoming, she would be the type to turn heads.
If they wanted to go more the brainy/nerdy Ultimate MJ route, with potential to become more like 616 MJ down the line, they should have gone with a look more like those pics above.
With Michelle, however, they went out of their way to deliberately make her look plain, frumpy, and unfashionable. They deliberately dressed her down and styled her down. Which fits and makes sense if her character is the type who doesn't give a crap about how she looks. Which may work for Michelle, but doesn't fit at all with Mary Jane Watson.
A Mary Jane Watson who doesn't care about her looks is like a Peter who doesn't care about studying and staying smart. It's counter and antithetical to the character.