Vegans may not be deficient but they certainly aren't anywhere close to optimal. That's why very few strength and power athletes are vegans or vegetarians.

People who concern themselves with building lean muscle mass, like me, do not seriously entertain the thought of plant-based diets, let alone high-carb ones. All of the data says otherwise: if you want to build lean muscle, eat quality protein that the human body will use most effectively. That means animals.

If you are a non-athletic, sedentary person then I imagine a vegan diet would work, though I question the use of the word "thrive".