I just looked that up, and I did find some advice that flossing addresses the food issue but not the issue of a bacterial infection not attached to pieces of food, which is probably also obvious. There are suggestions to use a water pick instead of flossing, which dentists have also recommended for a long time, but it's just not as available as string or toothpicks. It's not productive to tell everyone only to use the best possible solution if only 1% will actually do it.

So you have a good point, there are always new things to discover, but this is obvious in a way that's understood and doesn't in any way call into question the legitimacy of dentistry.

My point isn't that there's always new things to discover, it's that nature has so routinely made fools of us that the argument of "it's obvious" should carry little weight.