That is an apples and oranges confusion. (1) The fluoride in toothpaste helps in several ways but mainly by participating in remineralization of the tooth surface (only) after the “damage” of a typical meal. It also helps reduce some of the caries-causing bacteria in the mouth. (2) The fluoride in a municipal water supply is metabolized by the body in various ways and in growing children it gets incorporated into the growing teeth to make them harder and more resistant to decay. These two sources of fluoride are very different.
Your sentence starts out correct but then it goes south with your conclusion. Scientists have studied the effects of fluoride in water supplies for a very long time because plenty of areas have fluoride in their water supplies NATURALLY at levels which match (and even exceed) the levels those water systems which add fluoride artificially. So there is a great deal of data on various levels and their effects going back generations.
Now I’m fine with anyone who claims, “But I think the government set maximum for fluoride levels in water supplies needs to be studied carefully and lowered.” Indeed, about a decade ago, if I recall correctly, the government did indeed lower the maximum and set new guidelines for fluoridation procedures. If new data and more studies provide good evidence for making even more changes, power to 'em. That’s just good science. That’s how it works. As we learn more, science reaches better conclusions and explanations.
And the alcohol-based mouthwashes we know to be a very bad idea for the gums and for the oral biome. Moreover, fluoride in toothpaste and mouthwashes (unlike the low levels in fluoridated water) MAY when they are in high concentrations or frequencies of use seriously damage the oral microbiome that the human body depends upon for vital nitric oxide. (Some bacteria in the oral microbiome have the ability to reduce nitrate (NO3-) to nitrite (NO2-). And that leads to nitric oxide, which helps reduce blood pressure and reduce cardiovascular disease. I won’t try to list all of the other vital roles in the body. But one of my points is that perhaps more of your fluoride concern should be towards the high-fluoride rinses which some dentists prescribe excessively.)
I’m always for more scientific study of everything—but let’s not too casually assume that there is a reckless and blind use of fluoridation in our municipal water supplies. If it needs tweaked based on solid evidence, great. But let’s also admit that people have been drinking naturally occurring fluorides at various levels for a very long time.