Is heaty bad? Or is one better than the other? The answer is simply, "no". Seeing as the whole purpose of the classification is so that a person can achieve a balance in the foods they eat, it is obviously important for a person to consume both heaty and non-heaty foods.
The most interesting part of this theory is the ramifications a person will experience if they are off balance. Asians believe that many common ailments are caused by an imbalance in their diet. Things such as sore throat, fever, constipation, even a short temper will often be linked to their diet. And this is not some dying ancient Chinese theology barely being kept alive by the older generations. No! The majority of the younger adults my age, and children below believe in this. I once mentioned to a Chinese colleague that I had a sore throat and she said I must have been eating too many heaty foods, and she bought me a special tea that was supposed to put my diet in equilibrium again. This belief has come up among my younger local friends as well. When I try to laugh it off as some ancient Eastern orthodox medical philosophy, they argue and defend it saying that if they eat too much of a certain food, they feel themselves get sick.
My opinion: I do not doubt that many people feel that they get sick and perhaps even actually get sick if their diet gets off-tracked. However, as I do not believe there is any science to actually back this theory up, that this can only be explained as a placebo effect. Asian culture believes in this theory so strongly that it has become supported biologically. That because they believe that eating too much of a certain food will produce a certain undesired effect, that that actually is what happens.
Feel free to argue your opinion in the comments (be culturally sensitive!). I just thought this was an interesting cultural theory that many people are unaware of.