Ray, I think you are missing the forest for the trees to use an appropriate idiom. Let me try to be clearer about the key issue. It really has nothing to do with biomass increase except for certain crops such as grasses and perhaps trees grown for lumber where biomass is important. For row crops biomass may not be a good thing as we want those crops to orient production to seeds which means they need to focus energy on reproduction (which is what seeds are used for by the plants). If biomass production is reducing seed production that is not a good thing. Additionally, crops such as wheat and corn are carefully bred so that they have standability in adverse weather. If the crop is beaten down by heavy rain or hail then yields are reduced. If my rows of corn are producing lots of biomass but the stalks are too high and somewhat weak that is not a good thing. It's a tricky balance for the plant breeder to optimize growth towards seed production. It may be that enhanced concentrations of CO2 can augment seed production in a way that plant breeders can take advantage of but my reading of the literature is that this is not necessarily a given.
I can't quite believe you are making such an argument, Alan. Do you really think when researches discover that a doubling of CO2 increases the crop yield of wheat or rice, or whatever crop they are studying, they are referring only to the total biomass of the wheat or rice stalk, whilst ignoring any increase, decrease or lack of change in the mass of the edible crop yield?
It's always the yield of the food crop that features in their results. This is why many greenhouse farmers have been injecting CO2 into their greenhouses over many decades, for increased crop yields and increased profits.
At a basic scientific level, where results can be confirmed due to the controlled nature of the environment, whether in a laboratory or a greenhouse, the CO2 fertilization effect can be established with certainty, and with far greater certainty than the degree of any possible change in climate that might be due to current elevated levels of CO2.
However, it is true that growing crops in relatively uncontrolled conditions where one cannot always control the temperature, competing weeds and pests, and extreme weather events, then these other factor will influence crop growth whatever the levels of CO2 are. Temperatures which are higher than optimal for growth of a particular crop might partially or even completely negate any increase in crop yield that might have resulted under more ideal conditions, except with water-stressed plant. Under those conditions the benefits of elevated levels of CO2 are the most productive.
Are you still in denial, Alan?