Based off history, as much as I know you love them, I don't know anybody whose kept a long term successful tank with kessils alone. They are the most regretted purchase I've ever personally seen among people I personally know. Those who do well with kessil typically have to supplement their lighting. I don't see that with T5, Radions, AI, or any other manufacturer. I'm hoping the Kessil X will fix this issue.
Walk into any major vendors shop, which I can do in my area, you will not find Kessils. Two Guys Coral didn't use them, CaliKid doesn't use them, Reef Raft USA doesn't use them, Reef Lounge doesn't use them, Aqua SD doesn't use them, Battle Corals doesn't use them... Their clout is born from them being used at trade shows, where they offer free lighting to vendors. Outside of coral shows, where again, they offer free lighting as a marketing tool, none of the professional growers really use them.
Additionally, I believe they chose the lights they did for the growth experiment because they are the best option. But even then, even if they used nothing but THE BEST light at all times, I would find issue with it. Even though I don't care for kessil, the problem isn't using the kessil -- It's using nothing BUT the kessil. It's not a good way to show off other brands. And I'd have a hard time believing other companies wouldn't want their products being used unless it's in an X vs Y grow out format. Then it could make a company look bad due to lacking performance.
How many people buy the Giesemann verve? I'd wager not many... I haven't seen one in a single build thread by chance. I've only seen two orphek build threads. I've not seen any of the ATI LED fixtures being used (Full ATI LED, not powermodule). This is a great chance to show off different fixtures. And I for one would like more data on different lighting sources.