That is not what they said. You're doing the same thing the MPs were doing, insisting that the data says what you want it to say despite repeatedly being told otherwise. Partially, this was the scientists' fault by being polite and assuming people who ask them questions are smarter than they are. When they say "correlation", they think it clearly communicates the lack of strength in the data because "correlation does not necessarily imply causation" has been drilled into anyone working with data for a long time, though Professor Mareschal did attempt to explain this. I'm guessing you know that too, but because you think that damage is plausible, you too are willing to interpret this data differently than you would otherwise. Nonetheless, that's not the right approach.
Specifically, your "there's lots of evidence" parallel, no, not at all. The professors were asked to comment on the quantity of usable research, and they were consistent:
Blakemore: "What evidence do we have? Almost nothing. There are a few small studies, but they haven't been replicated, and they're purely correlational." (That one was in the article. Did you not read the article? Or maybe you don't understand why unreplicated research is a problem even bigger than correlational data? I have a feeling you know both those things.)
Dorjee: "As my colleagues have said, there isn't a lot of direct evidence that would involve brain scanning and could track changes in brain structure and function" (She goes on to describe things you can use, but since they don't involve saying "this is bad and I can show you on this chart", they kept asking for that instead).
Mareschal: "I know this is a mantra that there's very little information"
The MPs wanted, and your inaccurate summaries are insisting, that simple data exists. You're acknowledging that it's observational and not strong, but that's not what the professors were saying. They were saying that the data is inclusive and sparse even when you consider that observational information. They give plenty of advice about things you can measure which would suggest harms and ways to address them, but since they aren't as simple as at what age you stop blocking social media use, for which they were explicitly asked and refused, the MPs kept asking for that. Plenty of the harms they mentioned didn't work with the predecided plan because they indicated ongoing harm to adults as well, others because they suggested situational factors which a parent can manage but a law cannot, and still others because they suggested that harms weren't the same, sometimes less and sometimes greater, than the random guesses from armchair neuroscientists with no experience.