It's true that some of the commentary is specific to the full body MRI itself (such as misdiagnosis due to an imaging artifact), however many of the claims in the video are very general. And the scientific study they referenced at 6:30 has nothing to do with fully body MRIs. The study is in regards to thyroid cancer overdiagnosis due to screening (using ultrasound and not MRI). This is clearly a statement regarding the effectiveness of screening. And, yes, it is specific to the cancer.
I'm not saying anything that the studies aren't saying. For some kinds of cancers and for some kinds of screening methods, screening can result in overdiagnosis.
OK, so you had to watch a little more than ten seconds.
There's no doubt that some diagnostic tests - like getting a full-body MRI as a precaution - may do more harm than good. Your apparent mistake is thinking that means all diagnostic tests probaby do.
We'll have to figure out which one this is; it's a start of that process. We've demonstrated we can do it; now we have to figure out if we can distinguish between "big bad scary" cancer and "whatever it won't kill you" cancer.
At 6:30 it's about a specific test for thyroid cancer, which as discussed in my second paragraph, was not found to actually improve outcomes for that specific type of cancer, not cancer in general.
However, early detection is responsible for greatly improving outcomes in many specific cancers. Full body MRI is not the test to achieve that. GRAIL's gallery test might be one to do it for many classes of cancer, but that still remains to be fully seen.
The general of idea of early detection is still an extremely promising one for most types of cancer, and in particular for some of the deadliest, like ovarian and pancreatic cancer.
I'm not saying anything that the studies aren't saying. For some kinds of cancers and for some kinds of screening methods, screening can result in overdiagnosis.