You do you. Bold experimentation got many people at this site to the better place where they are now, so no one is going to deny your privilege to do the same. If you reach the grail and share it, we all will benefit.
But I'd be careful about putting too much stock in the quotes you provide here, since they are from a study of people who don't absorb vitamin D or absorb it very poorly -- "patients with malabsorption syndromes" as the article's title says. So it stands to reason that they can cite the research you mention showing malabsorption in these patients, but it doesn't say anything at all about people with normal absorption. One reason I looked at the study is that the quotes you provide so are contradictory to what has been observed time and again with the D3 regimen, where D levels go up significantly as people take more D3 (and not D2, which is the stated product in one of the quotes).
The "minimal erythemal dose" mentioned in one quote means "the minimum amount of x-rays or other form of radiation sufficient to produce redness of the skin after application, regarded as the dose that is safe to give at one time." You would have to create a whole lot of redness, or mild sunburn, all over your body day after day, to get to a substantial daily dose of D. The increases reported in this study from using the sunlamps for eight weeks might be beneficial to the patients in the study, but they are trivial in relationship to getting D to a level where it makes a difference for CH. Plus, it appears that the tanning machine (not cost-free) couldn't sustain increases.
Maybe the first quote, about sunlight, is accurate. But there have been many people here who have believed that their pattern of daily activities, from working outside to a lot of daily outdoor recreation or gardening, would have given them a satisfactory D level -- and were surprised to find out that they were at or below even the minimum level, let alone the substantially higher level needed to combat CH. I don't know what they are considering the "daily body requirements" in that quote, but the level of D required to combat CH is substantially higher than what medicine considers to be the "daily body requirements."
Like I say, bless you in your search for a "non-invasive & cost-free preventative." Something is working for you now, which is great, and who knows what you might discover.