One advantage that Eatwell may offer over an LC diet is that some foods based on wheat flour or cereals are artificially fortified for calcium and iron, and folate and B12. Meat products such as chicken get extras too but mainly cosmetic than nutritional, but also retain some vetinary interventions that prevent some animal conditions.
Certainly in my lifetime I have noticed changes in the quality of modern foods, such as milk, bread, eggs, but I put it down to mass production and batch farming methods. Although algae can be farmed usefully, most are cyanotoxic, and harmful. They thrive under poor conditions, and are not really considered as food. The algae blooms we see reported tend to be related to flood damage. runoff from farms, fertilisers with high nitrogen content, etc, and as a reaction to stagnant pollution,
The other aspect that seems to have altered is the frequency of thunderstorms. It is known that lightning plays a major part in the fixation of nitrogen into useful compounds used by plants, and this is also why farmers have to add man-made fertiliser in large quantities to augment that natural process. Now we get more rainstorms instead, and this gives a big washout effect that removes the nitrogen nutrients and topsoil, The increase CO2 also seems to reduce the uptake of nitrogen by plants, so using traditional crop cycling to replenish the land is not so effective, hence the annual muckspreading using sewage has become a major source of fertiliser, and the annual pong,