It's not meaningless, but it's an example of humanity chasing its own tail.
Photosynthesis is not the most efficient process in the equation by far. It is competing against two things; a system that can use lots of oxygen as an oxidizer to release energy, and titanic stockpiles of hydrocarbons waiting to be burned. An animal can either consume plants after they've done their job or consume other animals, and use animated lungs to consume a constant stream of oxygen that can be used to oxidize the energy substrate. Plants can only use photosynthesis, which is much less efficient of an energy transfer than respiration (creating molecules instead of breaking them apart). Because plants are stuck with photosynthesis as a food source, they are limited by its speed. Plants still need oxygen to respirate the food they create for themselves, but they cannot afford lungs and a cardiovascular system to utilize more oxygen. If they could, then they might as well be eating other organisms that already performed the hard work for them.
What I'm saying is that humans, being respiration animals, are always competing with plants, and do even more so when they release carbon from reserves in the earth. The ability of artificially propagated plants to compete against that system is minuscule. It can only compete with surface area, and for humans to be able to even make a dent in atmospheric CO2 by planting trees would mean planting way more trees than is likely worth their own expended energy. In such a scenario, the tables are flipped, and the animals (humans) are competing against the inefficiency of photosynthesis and must use enough energy to compensate. That is neither a proven strategy nor sustainable. Just as body fat can in theory be lost entirely through exercise, it is orders of magnitude more efficient to simply not introduce more energy into the system (i.e. consume less food, and eat food with fewer if any deleterious side effects).