'The fact that Adrien, who had the most reason to be angry at Ladybug for what happened in that episode but didn't is more than enough proof for why he's her partner.
This entire season has been about Ladybug learning how to be a leader, and Adrien struggling to figure out where his place in all of this was. The conflict of the season was that these two didn't know where they fit in exactly. Marinette wanted to try her hardest to be the guardian she needed to be and Adrien wanted to be the the hero she needed.
And in this episode both of them thought they lost it.
Adrien's worst fear that he wouldn't be useful for Ladybug anymore, and Mari's worst fear that she would fail as a guardian, both came true.
But all hope is not lost.
In this scene where Adrien comforts Ladybug, he does what he's always excelled at doing as Chat. Like so many other scenes, as I've mentioned in Miracle Queen, Psycomedian, Kuro Neko, and of course ladynoir in Puppeteer 2, Adrien's worth as a hero isn't determined just by heroic feats and clever planning.
It's because his compassion and empathy for others is what saves the day, time and time again.
He tells her to trust him, because he knows her better than anyone else. And he knows in that moment she needs him. It's this level of selflessness that is Adrien's greatest strength. He would never hold a grudge or be angry at her because at the end of the day he's going to be on her side, always and no matter what.
In the end he does what he was always going to do: he does his best for his lady. Because he knows what she needs, and he never hesitated to give it.
And Marinette, who has spent this entire season learning about what it means to be a hero, and failing because of trauma and making mistakes, has finally learned the most important lesson for her.
She is Ladybug. She is a hero, mistakes and all. Her fear and anxiety and trauma do not make her failure.
The people have faith in her and support her, they want to follow her. They love her. And that's what makes her a great leader. A leader who Paris can get behind even when everything becomes bleak.
There's this idea that Marinette has to be perfect to be a good Ladybug. It's an idea Mari has been struggling with all season. It's what has led her to make so many of the mistakes we see her make. It's what many of the fans have argued she should be, when the reality is Mari was never perfect. Just like with Adrien, the show tells us that perfection isn't what we're looking for. It isn't what we need, it isn't what Paris needs.
What Paris needs is these two who never give up and always fight, who get back up even when they fail. Who the people want to support.
We've hit rock bottom now, the lowest of low. But the one thing this episode showed us was that Adrien and Marinette are the best Chat Noir and Ladybug for the job. And most importantly, it reminds us what makes them the best team for the job.
And that they most certainly are a team. Ladybug, Chat Noir, and all of Paris.