Its exactly the opposite. Plants grow larger with higher CO2. And they also reduce in digestive quality significantly as more of the material is lignin.

> At the levels of concentration of CO2 we’re seeing, plants are decreasing in size. Trees grow smaller.

No, they don't. Not due to CO2, anyway (maybe temperature, or changes in precipitation for particular plants).

Even if you want to (inaccurately) argue that specific plants will grow smaller, abundant CO2 will lead to more plants.

> There’s a balance to how much CO2 plants can adapt to and absorb while maintaining their growth and yields.

Again, no. Plants are limited by their genetics, and the availability of inputs, one of the most important of which is carbon. CO2 does not limit a plant's growth. That's just silly.