Okay, before I start- I don't like the term creator's pet, it tends to suggest currying favor on the 'pet' part, and obviously Marinette or Adrien can't do that.
Perhaps 'favorite'? and let me lay some ground rules.
This is not character salt! Nothing here should be used to deride the characters. This is about the narrative woven with/around them. This is examining the external biases at play.
We must recognize that Marinette is the PoV character for the show. That is value-neutral. We can't hold screen time as evidence.
That said let's tackle Adrien being 'perfect' first. I know the show and creator use that word a lot but it is very clear in the show that ... He's not. He makes mistakes, he gets *called out* for his mistakes, he gets upset, he apologizes. He's not perfect.
So, why/how/what is the purpose of the perfect mantra in the show? It's because Adrien is a *trophy*. He was Gabriel's trophy, and now he's Marinette's. A trophy must be 'perfect', or how can it be a trophy? He makes no demands(his flirting as Cat Noir was shown as him being wrong and he corrected his behavior to be more perfect), he gives everything, he carries emotional baggage and costs nothing.
All of his perfection benefits *other people* in the narrative, not himself. Does that sound like a favorite? No it sounds like something you *give* to your favorite.
Because yes, I do believe Marinette suffers from an above-average attachment by her creator(and some fans) I say suffers from because I think it hurts her as a character. Superficially it seems to her benefit, but below the surface it's empty calories.
Marinette makes mistakes too, but they are always framed as best intentions. At the end of any disagreement she is the one in the right. Her pain is always the focus/valid one in any situation. S5 amped this up to the point I call it 'Poor Mari' when it happens. Any emotional situation must make you sympathize with Marinette first and often only. It doesn't matter what or who is involved. The entire Agreste Arc has been summed up by the emotional impact *Adrien's family being the villains and his father dying* have on *Marinette* not Adrien. Marinette gets the sympathy for someone else's crisis. How weird is that? It's not even that she did anything wrong (before the lie) but no one else seems to be allowed to experience more emotion than she does, no matter the situation.
That is a strange choice and one that hurts the narrative and her character. (As they find new/more/repeat ways to put her in emotional turmoil to keep her always center all the time)
As an example from before S5, we can look at how Luka/Kagami were handled. It's two parallel situations, handled at the same time. How they're handled gives the insight you are asking for.
Marinette's struggle is the first an foremost thing in Truth. Luka is the sweetest bean, and even when he's akumatized it is all about her pain the end and her having to break up with him. He's upset but he never blames her, never corrects her. After the breakup he is still completely supportive and always there. He works to find her happiness, even though he openly admits to still being in love with her. Marinette is handled gently and put on a pedestal.
Meanwhile, Lies focuses more on Kagami and her efforts to connect with Adrien who is pining for Ladybug( just as Marinette is pining for Adrien) She gets mad at him. She breaks up with him. She holds him accountable for his behavior. She gets over him. When she finally joins team Adrienette it is for *Marinette's* sake, not Adrien's. (MP72)
So yes, Marinette is favored heavily, beyond simply 'the main character' she is the center of this world physically and emotionally in a way that is only more noticable as time goes on.
Oh- and another easy metric: How many people have said Marinette is the best Ladybug ever vs. has anyone ever given Cat Noir the time of day except Ladybug when she felt bad about leaving him out of the loop?
