I will argue in favor of plant-rich diet but not 100% plants, here is why.
Indeed, plant-based diet can fulfill most of the nutrients that our body need daily, rather it's the macros (Carbohydrates, proteins, & fats) or the other type of vitamin and minerals.
But, there is no plants that contain B12 that our body need to maintain the function of our brain, so we need the food source from either Dairy products, Fish, or insects.