[flockonus]

> Another theory is that a perfectly-absorbing leaf would somehow absorb too much energy and get overheated

If having both pigments means the plant would be close to black, overheating is an absolutely valid hypothesis imo, plants just like animals have optimal temperature metabolism and often getting too hot is deadly, while under optimal temperature is tolerable.

[geokon]

sure but there are probably ecological niches that are light starved. for instance deeper in the water column or in dark areas like caves or polar regions

[Theodores]

Evolution is only possible along certain paths, for example, we are not going to evolve to have more than four limbs, eyes at the back of our heads or extra hands.

Similarly, at the cell level, we have just the one photosynthesis process in plants and that isn't going to take an entirely different path to work on different wavelengths. The evolutionary investment is in chlorophyll with a magnesium element at the heart of it. Imaginably you would need an entirety different molecule with some other magic atom in the middles of the usual organic chemistry and that isn't going to happen given the sunk cost in the chlorophyll way of doing things. There is a greater chance that we will get six hands than that happening.

[flockonus]

Of course, for example several sea weeds come to mind in dark green to brown tones; which makes sense, they can disperse heat very fast since they are immersed in cold water / liquid cooling

[prerok]

Indeed, and frequently you will see that leaves are a much darker hue of green than the ones exposed directly to sunlight. So, using the same mechanism, still more is absorbed if light is scarce.