I agree with you that acidity is the main cause of enamel erosion. The correlation between beverage acidity and tooth decay is such that I think we should highly discourage children from drinking any carbonated or acidified drink .

I disagree that "pH of 5 is 10x worse than 6, 4 is 10x worse than 5 or 100x worse than 6". pH is logarithmic with respect to hydrogen ion activity but hydrogen ion activity is not linear with respect to enamel erosion in a human mouth [1].

[1] https://www.sciencedirect.com/science/article/pii/S199179021...