True, but I'm willing to bet that N deficiency is pretty wild spread world-wide, including in natural soil. Probably the second dominant stunt factor on plants (after water), and way before CO2.
Yes and no.
Nitrogen deficiency is the factor that would promote the most growth, but at the same time, it's fair to think of all plants as constantly CO2 starved.
We would be pretty miserable at 800ppm CO2, but plants would love it.
All of water, CO2, and nitrogen (not an exclusive list) can stunt growth, and increasing the levels of any one of them can accelerate it.
Your own link points to this, referring as it does to the "most limiting condition", and the fact that addressing P and K deficiencies also increases yield, but not as much as also addressing deficiencies in N.