That's what has confused me as well. If you look at a bottle of Faygo it's got anywhere from 1.5x to 2x more sugar on average compared to coke, which almost makes you wonder how fucked up his maw must be that it's inconsistently sensitive. I recall that some of the video calls that Cassandra posted revealed that he was eating spicy foods, like the Domino's sandwiches. Maybe his mouth is just fucked up in a very specific way to where his nerves are ONLY sensitive to heat, like how some people can't bite ice cream or drink iced drinks due to teeth sensitivity. So like anything above body temperature is an absolute shock to his nerves. I mean he's shown that he loves his sweet tea and he has no issue eating spicy foods outside of his spice tolerance. If you've seen the video where he picks his teeth with a fork, or where during the spicy noodle video he hits his teeth with the utensil, it shows he isn't feeling a strong enough reaction to hard objects against his teeth that make him recoil. So the issue can't be stuff touching his teeth but instead has to be related to his chewing.
I wonder to what extent he's been lying this whole time about heat sensitivity in order to get out of eating foods he doesn't like. He might just be a super picky eater who only enjoys a set type of food, like how some autistic people will refuse to eat anything outside of a set few dishes, so when presented with something outside of his usual slop he just won't touch it and uses "letting it cool down" as an argument. I think about the story Gordon told about taking him out to a restaurant and him barely even touching the food he was given. It might just be that the reason he eats hot pockets and canned food is because he doesn't like anything outside of that range.