That's not what I meant at all - there are plenty of other non-meat sources of protein, from cheese to nuts, depending on how vegan you are. Once again, what I'm taking issue with is the notion that because 8 units of grain are needed to provide 1 unit of beef, the units are nutritionally identical. Making weight for weight comparisons as above is what's a non-sequitur.
Getting such comparisons fully correct is certainly hard, but I don't think it goes the way you think it does in this case... looking at a few different specific possibilities for "beef" and "grain", the "grain" looks to usually be nearly twice the calories of the "beef" per pound. Humans do not actually need huge amounts of protein and there is rarely a (medical) need to go out of your way to get protein no matter what your diet is.
