Maybe it's half of what you eat, but I've been "allergic" to nightshades my whole life and never felt lacking in options (I have a mast cell disorder, tomatos, potatoes etc cause anaphylaxis, it's not a true allergy, but it functions like one)

I can eat practically anything, it's only like 20 plants I'm allergic to out of like 700 I have available to me. And if I travelled overseas I'd find more stuff I could safely eat there too.

I just can't eat much pre-made, packaged organic convenience foods. Most will contain potato starch, unmarked dextrose, "spices" (if it's not specific in the ingredients list, often I avoid), etc

Even desserts aren't safe because e160c, paprika, is what most companies here used when they swapped out the red dye 40.

So I cook from scratch, but I've never felt limited in my own kitchen because of the ingredients I have. (I am limited at restaurants, I usually order a black coffee and enjoy my dining friend's company)

I also don't live in the America's, so that helps. I can see why they would think nightshades are everything, all the best foods from the Americas start with tomato, or capsicums, and potato is a staple carb. Meanwhile my cultural diet is based on brassicas and oats.

But at the end of the day, Beans and rice is nightshade free, it doesn't take a genius to think of a non-nightshade vegetable to add to the mix to make a unique meal.