It seems pointless arguing about health benefits of diets, seeing as it's pretty easy to trawl the internet and find different studies pointing to positive and negative effects of all diets whether high carb, low carb, paleo or vegan or whatever. The only thing that seems clear is that a standard junk food / processed food heavy diet is bad for you whereas one made up of lots of whole foods is good.
Most people who are vegans, or mainly plant based, don't choose the diet for solely health reasons in any case.