And even then, the pairings you mentioned only exist because of the convenience of commercial agriculture lol.
How about the old classic trio of
corn, beans, and squash? As I learned it, these plants complement each other both agriculturally and nutritionally.
Wiki:
The three crops benefit from each other. The maize provides a structure for the beans to climb, eliminating the need for poles. The beans provide the nitrogen to the soil that the other plants use, and the squash spreads along the ground, blocking the sunlight, helping prevent the establishment of weeds. The squash leaves also act as a "living mulch", creating a microclimate to retain moisture in the soil, and the prickly hairs of the vine deter pests. Corn, beans, and squash contain complex carbohydrates, essential fatty acids and all nine essential amino acids.
Just because a modern balanced vegetarian/vegan diet would not be achievable 5000 years ago, doesn't mean very much. There are plenty of foodstuffs and supplements that can provide the nutrients that a strict vegan diet lacks - for instance B
12 can be found in some mushrooms, seaweed (purple
nori is apparently a good source of B
12[ref]), algae, and fermented foods like tempeh or natto. Still, you have to go out of your way to include such a source in your vegan diet, and such sources are more expensive and less accessible than meat (or even "synthetic" vitamin supplements).
In my opinion, a diet consisting mostly of plant material with the addition of moderate portions of meat (ideally whatever's on sale at the time) will fulfill all your nutritional requirements while also allowing some opportunities for creativity. (I don't know about you but I find substituting tofu for meat leaves a lot to be desired.)
Sometimes people gravitate towards vegetarianism for an economic reason, that is to say, it is much cheaper to prepare a meal of vegetables rather than a meat-based meal that could cost many times more expensive (A plate of rice and beans costs under a dollar, while a middle-of-the-road rib eye steak
alone is easily $5 or more, minimum). However, there are plenty cuts of meat to choose from. If you know what you're doing you can easily make a delicious entree with the cheapest cuts. Spend the $20 on ground beef instead of a filet mignon and you have dinner for a whole week.
Oh also, try to find a bespoke butcher to buy your meat off of. Not only can you ask for specific cuts of meat, but they can tell you what's good. Try getting some chuck steak or brisket ground into burger - you will never buy supermarket extra lean ground beef again.
