Lentils, chickpeas and beans are the best sources of proteins among non-processed vegetables, but they still contain too much starch and it is impossible to use them exclusively to provide enough proteins within a diet of not more than 2000 kcal/day, suitable for a sedentary life style.
They are necessary for a vegan diet, but they are not sufficient. They must be combined with some other source of proteins, which must contain much methionine and which must have a better ratio between protein content and calories.
The commercial protein extracts from them are much more expensive than meat, so they are a non-solution.
> but they still contain too much starch and it is impossible to use them exclusively to provide enough proteins within a diet of not more than 2000 kcal/day, suitable for a sedentary life style.
Lentils have 26g of protein and 353 calories per 100g, and eggs have 13g of protein and 143 calories per 100g, so the ratio is 13.5 for lentils and 11 for eggs.
Whole eggs, like also most kinds of dairy, have similar amounts of fat and proteins, so indeed they are not much better as sources of proteins than nuts or seeds.
On the other hand, lean meat is almost pure protein, so its ratio of protein vs. energy is 3 to 4 times better than for vegetable sources.
Even with whole eggs, you can get much less calories than with lentils, if they are used to supplement cereal proteins, because they have a significantly better lysine to calories ratio, so when the amount of required lysine is specified you can eat less of them than in the case when their amount would be computed to provide a specified amount of protein.
An adequate daily protein intake from food cooked from vegetables that have not been processed using special methods for protein separation would provide over 3000 kcal/day.
Using so much energy requires many hours of intense physical activity. When your job requires spending 8 hours or more per day sitting in front of a computer, then it is absolutely impossible to also do enough physical work to consume over 3000 kcal.
Therefore your suggestion is also a non-solution for many people.
It is true however that for most of our ancestors the problem of gaining weight when eating a strictly vegan diet would not have existed. This is indeed just a modern problem, of the sedentary people.
For instance, bread is normally considered to be an incomplete source of proteins, but that is just because one cannot eat enough. Eating bread made from 1 kilogram of flour per day provides enough of all essential amino-acids. It also provides about 3500 kcal/day. Someone doing hard physical work, like it was much more common in the past, could eat only bread without needing any other source of proteins.
You can use a lot of words, but it doesn't change the underlying fact that you're too lazy to make your dietary principles really work. Burning 3000 calories a day while working in software is absolutely possible. I did it today.
They are necessary for a vegan diet, but they are not sufficient. They must be combined with some other source of proteins, which must contain much methionine and which must have a better ratio between protein content and calories.
The commercial protein extracts from them are much more expensive than meat, so they are a non-solution.