You must not have looked. Almost all (except for commercially funded) studies prove plant-based diets are much healthier; it's literally the scientific consensus in nutrition.
Otherwise, there are plenty of studies that show that those vegans who neglect to take appropriate supplements have various health problems, e.g. osteoporosis or anemia.
I also have heard of many (and I know personally someone) who were forced to abandon the vegan diet after some time due to health problems, but it is very likely that all such problems have been caused by not taking a complete set of supplements, because most have heard only about B12, and that is not the only substance missing from plants.
Non-vegans have just as many nutritional deficiencies, if not more, like a total lack in fiber. And for every neglectful vegan, there are ten unhealthy animal product-eating individuals with even more debilitating diseases, like diabetes, for example.
Also, DHA/EPA is synthesized in the body; it's not necessary to supplement them, nor any other vitamins you had listed, other than B12 and possibly D3 (depending on your latitude).