I don't contend that supplemental Vitamin D3 is as good as natural Vitamin D3 from sunlight, nor do I propose that anyone take Vitamin D3 to avoid sunlight (which has other benefits beyond producing Vitamin D3) any more than I contend that most vitamins, minerals, enzymes, phtyo nutrients, etc., are better in supplemental form than they are from natural food and plant sources. However, when you can't or don't get enough sunlight, there may well be a price to pay unless you supplement.
I would say that rather than being too good to be true, Vitamin D3 is too good to ignore. Other than that, I have said what I will here - there have already been far too many drawn out threads and debates on the subject.