There's also the other ramifications of increased CO2 concentration like: ocean acidification, warmer overall climate globally and increased incidences of severe weather, rising seas resulting from the warmer temperatures, and not all plants will enjoy the higher temperatures (or the droughts, hailstorms, strong winds, too much rain all at once), especially those in the tropics which already get quite warm.
>Our results suggest that future climate change will push this ecosystem away from conditions that maximize NPP, but with large year-to-year variability
[0]http://www.pnas.org/content/pnas/early/2016/08/30/1606734113...
edit: less blunt.
Here is one of many scientific papers on the subject: "Carbon dioxide starvation, the development of C4 ecosystems, and mammalian evolution" [1]
[1] http://rstb.royalsocietypublishing.org/content/353/1365/159
>Global expansion of C4 biomass is recorded in the diets of mammals from Asia, Africa, North America, and South America during the interval from about 8 to 5 Ma.
That's a 3 million year period, ending 5ma. You say CO2 starvation is down to 150ppm, but atmospheric CO2 levels have fluctuated between 180-200 (ice ages) to 300ppm (warm periods) for the past half million years or so.[1] Meanwhile C3 plants (those supposedly which suffered during your linked expansion of C4 biomass) are around 95% of plant biomass currently. Doesn't seem like plants on the whole are starving for CO2 at this time.
I'm impressed by your method of argumentation.
Land-based plants evolved when CO2 levels were much higher than today. [1] In fact levels have been steadily declining from 3000 ppm 150 million years ago; the current, holocene rise is a relatively minor bump. [2]
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1692178/
[2] http://caos.iisc.ernet.in/faculty/pghosh/content/Publication...
At current CO2 levels plants are starved for CO2. At 150 ppm there would be a massive extinction of land-based plant life.