Was stuck between A and B and went with B.

Hi, when I read this argument I actually had a similar thought. The author seems the be treating the idea of dissolving as being equal to not being in contact with teeth, and they seem to treat the idea of food being in the mouth as equal to food being in contact with teeth, both of which feel like questionable reasoning to me. Surely a dissolved liquid can still be in contact with teeth! This is indeed a flaw of the argument. However, I think there's another flaw, which as you noted is the baseline rate. Caramel is basically pure sugar, which causes more cavities than the wheat that makes up a pretzel. An argument can have more than one flaw to it, and I think it is helpful to recognize that once you've located a flaw there may still be other issues with that argument. Additionally, A is really tough to understand. I think it would take a few steps to directly connect A to the idea that caramel and pretzels may have other differences that matter (sugar content) than rate of dissolving. To be clear I don't think you're overreaching at all, and poking as many holes as possible in an argument is far from a bad habit.