I have yet to see any empirical evidence that proves one light technology has any advantage over another when it comes to potency. We've seen lab results that favor LED, but we've also seen lab results that favor the different types of HID. For that matter, you'll find a lot of HPS growers who claim to achieve greater potency under fluoros, but opt to stick with HPS for the many obvious benefits it has over something like T5s. There are far too many factors to draw a firm conclusion based on anecdotes. I believe that it comes down to personal experience, so if a grower feels that they are getting better results with any one light, more power to them, and may they continue to have great success. For my part, the weed I'm growing under LED unquestionably matches the perceived potency (and flavor) of any weed I've ever had, from any source.
I agree, anyone making claims that weed is higher THC under CMH, HPS, LED or anything else is looking at one grow that went well and comparing it to a different grow that didn't go as well.
I grow with LED PCB builds I did myself, and I have grown with Nanolux DE's. Both grow about the same as there are many factors that effect a grow to where a perfect side by side is simply not possible. In the end the LED are near 2x as good because they use almost half the energy to get the same results... Less heat, more room due to a lower profile, less degrading of the light source so no replacement bulbs and so on... It's very possible that LED in years to come might br using 30% of the power of an HPS for the same grows, at that point LED would be 3x as good as HPS, but that does not mean HPS can't grow equally as good weed, it simply does it with a lot more power, heat and so on.
I like LED because odds are they will get better and better while HPS stands stagnate. I like knowing that in years to come I can simply switch the diodes on a new build and have even better lights without paying someone else to make, advertise and sell the same light I can build myself.
As it sits I can build my lights for about 290$ a light, it takes 2 lights to equal a HPS but I get better spread of light... so in just one year my led lights are cheaper to build and run over buying a Nanolux/gavita, a bulb to keep yields up and near twice the energy consumption.
Better weed? hard to say.. I believe weed grown under my LEDs looks better but I think it's because it's harder to burn my plants, less heat so tighter buds and I can get WAY more purple-ing with my LED. But more THC? I doubt there is any difference.