We are not 100% TF (esp. as we're vegetarian) but we do eat organic, pastured eggs and butter, that good stuff. DS and DD1 have perfect teeth, DD2 has weak enamel on her first four top teeth.
They've remineralized now but I ascribe it more to the xylitol and MI paste than to dietary interventions although I definitely upped her intake of pastured ghee, eggs, etc. There's so much to the picture, I don't think you can isolate any one factor. In DD2's case, the fact that her top four teeth have this problem but none of the other 12 she has so far to me indicates that something happened while they were forming -- perhaps a fever while she was in utero, perhaps the IV abx she got in the NICU (no choice there on my part).
There's so much individual variation in saliva acidity etc. that affects the constant demineralization/remineralization process....
That said, I think dietary choices can definitely play a role either in the eating of/abstaining from certain foods or the timing of eating them. For ex. eating carbs of any kind before bed without brushing and then nursing all night = big no no as fermentable carbs plus breastmilk = very bad for teeth. Even without the nighttime nursing issue, fermentable carbs on the teeth can lead to decay-causing bacteria reproducing right quick. But eating eggs and cheese = totally fine not to brush afterwards as they are anti-cavity-forming foods. So a diet high in fermentable carbs, in a child who's vulnerable for whatever genetic/developmental reasons, can lead to more problems than a diet high in non-cariogenic foods.
I agree, there's no magic bullet and it is way too simple to claim that a certain diet guarantees good teeth.