I agree with you on losing overall output when trying to gain efficiency. Its a trade off choice that every
led manufacturer has to make. When driving the diode harder you have to ask yourself how much am I willing to do for 10% or 5% more light while using 20% more energy. The harder you push the less you get in return. They may make different choices for different
lights within their own product offering because of available/cheap parts. I would bet that often times they end up making poor choices that don't really make sense.
As far as for plants though I disagree that PAR isn't the whole story. It doesn't matter how many photons you put out if they aren't at a wavelength that plants cannot utilize for photosynthesis. To compare two light directly for effectiveness on plants you woud use a quantumn light meter to measue the Photosynthetic Photon Flux Den- sity (PPFD) which according the meters manufacturer is a measure of PAR light, and boy do I need to buy one :-)