If i went with a commercial fixture, i would have got two Sbreef planted tank, which combined is 300+ watts, which is roughly equivalent to the 350 watt power supply i am using. These cxa1304s are run at 750mA and only using about half the supply. From an output perspective, this would be like spreading a single sb reef over a 75 g tank.
The goal was to be able to have the fixture as high above the tank as possible. The farther the lights are from the waterline, the less variation in par through the water column. This stand could also support a 90g tank in the future and the lights would be suited to that.
Also, more leds run at lower power means more uniform lighting. Also, design constraints meant either two or four drivers for the whites. I dont believe two drivers / 12 cxas would be adequate, and three drivers presents awkward organization. Iow, you are unaware of all the factors i considered when designing this.
Based on wattage of commercial high par fixtures, this is not overkill, it just has suffiecient headroom for taller tanks or to grow carpets.
I'm not trying to discount the planning you've put into this, as I've read all of the threads you've posted regarding each aspect of its design. I'm trying to give you real world measurements (now that I have them) using similar COBs that you can use to correlate PAR numbers in your tank setup. I suggest grabbing a $20 LX-1010B lux meter from ebay to get numbers for yourself, but as it seems you're penny pinching with this build I thought you'd appreciate some non-theoretical data to work with.
As another point of consideration, the black-box-tier lights use unknown cheaper diodes with less light output efficiency, and the quoted power consumption numbers take into account ~80% AC-DC conversion efficiency and 80-90% LED driver conversion efficiency, so that 300W power consumption is only 210W to the LEDs, which may be 60-70% of the efficiency of CREEs, so equivalent power would be around 150W of crees.
To correlate back to the original data I gave, you can assume a 75g is split into 3 16x18x21 cubes similar to mine. You have 8 LEDs per cube, but the cubes are taller. Throwing the data into spectra gives ~100PAR at substrate ignoring refracted light, so when starting the tank, 20-30% would be a good point to begin at.
EDIT: Read the recent replies. I'm interested in comparing the spread of my new soon-to-be-75 fixture, which has two clusters of FF/3000k and reds/blues that are sitting ~18" above the water level, to your spread-out 1304s.