Many of the "simple ingredients" that people used 100 years ago aren't really available anymore, at least not in the US. That would somewhat true even with traditional breeding and cultivation, but over the past 100 years we've greatly improved our understanding of how breeding works, the rate that we can modify plants and animals, and with GMOs we now have a lot of direct control over the outcome. We just don't have the same plants and animals that we had 100 years ago anymore.

You say you stick to organic/natural. Well, it's all "natural", even GMOs, if you're eating plant and animal products directly. (Eg: stay away from additives and highly processed foods.) "Organic" is a bit tougher; you want it to mean that the plants and animals were raised without getting stuffed with chemicals and antibiotics, but there's a lot of wiggle room there because 'food' is made up of chemicals, and many foods and chemicals have some antibiotic properties.

In the end, if you're not growing the plants and breeding the animals yourself you don't really know if the "organic" label on them means what you want it to mean. And except for heirloom varieties, (and maybe even those) the plants and animals you're raising are still the product of the past 100 years of breeding, which usually focused on attributes other than making them healthy to eat.