I'm not necessarily arguing it's untrue, just not quite the hard-and-fast rule that 1 is.
This is pretty subjective. If you grow up with sufficient dietary iodine, that's worth 10-15 IQ points (a gigantic amount) compared to the counterfactual. Iodine supplementation is highly effective in populations that have presumably been going without for, at the very least, many hundreds of years. This is the reason we iodize salt.
With that in mind, how much of a hard-and-fast rule is #1?
The other side of this argument is that dependencies can be surprisingly subtle. This is pure speculation, but the thing that leaps out at me about atmospheric nitrogen is that oxygen is extremely corrosive. If the atmosphere were more oxygen and less nitrogen, lungs of today might experience a lot more wear and tear than they are currently designed for. (Or not! I really have no idea. But I think the hypothetical has some thought-experiment value anyway.)