Sedan, you are assuming that CO2 is the only limiting factor, it is well known and proven that plants will reduce the number of stomata to reduce evapotranspiration when there is adequate CO2 around.
I can have a bigger fuel tank in the car but the carby is what feeds the engine and plants are no different. They will only take what they need depending on the limitations of other necessary sustenance.
Also yield is not what we need, we need protein.
It is true that in past warmer climates there has been supposedly more vegetation ( I was not there) but that is due to a wetter and warmer world, not more C02. There may have been more CO2 at the time but that is not what made more vegetation, it was the available water.
