My mistake, I had blindly dismissed rice since it is commonly known to be a nutrient poor food. But several sources confirm the parent post and your comment are correct*. It's also too often repeated that a vegetable based diets will be lacking essential amino acids which seems like a gross falsehood now if you can get there with two wildly available plants that make up a common low-cost meal. I am baffled by the disconnect.
*I don't cite the source since I am unsure if there are caveats or if the claim is controversial.
I think the disconnect is that for meat you don't have to think about it. When it comes to plants, suddenly you have to know something about what you are eating. There are plenty of plant diets that are viable, you just have to research a little bit.
Everyone always mentions beans and rice, but Potatoes by themselves are a complete protein. Some of the essential amino acids aren't found in high quantities in potatoes, so you have to eat a lot of them if you go that route. They are missing some vitamins and minerals as well, so you have to add sweet potatoes if you don't want scurvy.
*I don't cite the source since I am unsure if there are caveats or if the claim is controversial.