Why aren't plants black? 🌿

One assumption you seem to have made is that green-absorbing chlorophyll is possible, and therefore an evolutionary choice. If you look at the molecule you can see that it's basically a compact photon antenna, and any simple chemical change will shift the band-gap in a discrete jump that seems to miss green entirely. 

Anything more than a simple change reduces the efficiency; so perhaps asking for green chlorophyll is like asking for a standard silicon diode with a custom band-gap; sorry, but quantum mechanics says "No".

So it's not about life evolving to make maximum use of the available energy - it's about taking advantage of the molecule with the greatest conversion efficiency, which in this case only comes in red or blue. Retinal does what you suggest (absorbs green) and some think it even came first evolutionarily, but it has a lower efficiency than chlorophyll.

Then you've got waste heat from the conversion to get rid of, and that takes extra systems... it becomes a whole thing...