That would be worth something in a debate, where truth is the goal.
But this isn't a debate, this is a decision. The agent is Meta. The field is their products. The goal is reduced teen mental health issues. And the buck stops with Zuckerberg.
"Correlation does not prove causation" alone is not an excuse to avoid an action. It is a principle that can be used to compare actions for how likely they are to achieve the goal, and so it must be combined with some other action and evidence that makes that other action appear more likely to work. Without that, then the action suggested by the correlation remains the action most likely to work, and so it must still be taken.
If, for whatever reason, Zuckerberg doesn't want these changes to be made, then he needs to either dole out resources to gather the evidence he demands and which may free him from them, or he needs to implement some other action which may turn out to work.
If he doles out the resources, and the evidence comes back and establishes causation, then he has to make the changes. It sucks for him, but the goal isn't to please Zuckerberg, it's to reduce teen mental health issues.
If he doles out the resources, and the evidence comes back failing to establish causation, then that's convenient for him. But he still has to try something else, because the goal is reduced teen mental health issues and it has not been achieved.
If he goes straight to implementing some other action, and it at least appears to work, then he doesn't have to make the changes he didn't want to make. That's great for him, and since teen mental health issues were reduced, he can put it behind him.
If he goes straight to implementing some other action, and it doesn't work, then still has to try something else, because the goal is reduced teen mental health issues and it has not been achieved.