1. The "studies" that claim that a plant-based diet reverses heart disease are lying. True studies have concluded that there is no difference in cases of atherosclerosis between vegetarians and meat eaters. If you only consider the facts behind fat intake and how it affects the body, it becomes apparent.
2. Your problem is that you've confused cause and effect.
Let me guess, you weren't just a "big steak eater". I bet you ate a lot of junk too. Carbs, sugar, processed foods, the whole shebang. Then you made the right choice to begin eating healthier. I bet that you not only gave up meat, but you gave up a lot of other foods as well on your path to nutritional awareness?
That's why you lost weight. That's why you became healthier. It wasn't because you gave up meat. It was because you became a healthier eater overall and chose a healthier lifestyle (i.e. you quit smoking). Even vegetarianism is better for you than the "typical American diet". Also note that the "steak" you were eating before came from animals which were fed genetically modified grains and were injected with harmful chemicals and hormones (all of which you were indirectly digesting).
3. Your new found physical ability has nothing to do with health. I've known "physically fit" marathon runners whose diets consists of bread, pasta, sugar and ice cream. You should also know that intense aerobic activity is counter-productive to health and runners tend to eventually experience heart problems.
4. If you are living animal-flesh free. You are not healthy, whether or not you feel like you are. It's that simple.
You are not getting enough saturated fat, vitamin B12, iron, beta-carotene/vitamin A (unless you're eating tons of butter), and vitamin D. Eventually, these deficiencies will come around to bite you.
A proper diet consists of adequate amounts of (natural) meats, vegetables, and fruits while avoiding grains, sugars, and other processed foods. We are omnivores. Why do you think human beings have incisors? Just for looks?
Just take a look at all of these examples of people who have found true health through true nutrition. Are all of them killing themselves with meat?