It made me remember an article I read in 2015 which claimed that plants should be purple, because green light carries the most energy (and green plants reflect green light).

Then maybe they should be black and absorb all visible light? No. Producing pigment is quite energy intensive, so alternatives mainly pop where a niche forms due to competition for resources. That's why brown and red algae are a thing the deeper you go, as with depth the composition of light changes to that of blue and green. And because the light intensity changes as well, efficiency needs become dominant.

In any case, plants ignore the most energy-rich part of sunlight because stability matters more than efficiency, according to a new model of photosynthesis. And it makes a lot of sense, intuitively. Even in lab-scale chemistry it's often advantageous to take a longer process at lower temperature to obtain, for example, higher yield or optimise for a specific isomer or what have you.

Back in the day, all the tiny light-eating lifeforms were purple. Being more efficient overall, the “purple gang” greedily sucked down all the light they could get, and grew and multiplied as quickly as possible.

"Back in the day" was about 2.4-2.6 billion years ago, and the oxygen wasn't even remotely as abundant in the atmosphere or water as it was after the Great Oxygenation Event, so creating purple retinal:

was preferable since it only needs one oxygen atom per molecule. Chlorophyll, varied as it is, needs at least 5-6 times as much, and even more of it for it to be produced with any level of certainty because of reagent proximity being ruled by thermodynamics and statistics. While on that, the composition of the atmosphere was different and there was no ozone layer, so that life was bathing in a lot more UV than it does today. The author compares apples with oranges, to put it coyly.

EDIT: Some style/grammar corrections, added a few facts.