You can lose weight on any diet, Veganism is just one of the very best.
The three articles you posted are on how switching to a vegan diet makes you lose weight, but the problem is that a healthy diet isn't solely about losing weight. This is what Darryl is trying to say, but that tunnel vision of yours keeps shining true.
The truth is that yeah, veganism can make you lose weight if you're eating a lot of unhealthy, carb/sugar-rich foods, which a majority of overweight people already do so take that as you will. But this isn't helpful advice because everyone already understands that cutting out unhealthy foods can help you lose weight and people with actual weight problems will NOT be helped by switching to a vegan diet alone.
I think you need to crack open a human biology book sometime and read up on weight gain and loss, and how our body stores fats. I don't think you can really argue his points considering he prolly knows more about the whole dietary habit deal than you