Why do you feel qualified to offer medical advice like this? Are you a medical doctor?
Statistical illiteracy is widespread among medical doctors.[1] There's no reason to trust a doctor to interpret a p-value. For these types of questions you're much better off listening to a data scientist because they have actual training in interpretative statistics.
It's about understanding and processing this evidence in the broader context of their medical training. You're trying to generalize the results of a study with many shortcomings to say everyone may be better off dealing with increasing their odds of developing malignant melanoma and dealing with its associated mortality risks.
My issues with using this study to give the above advice:
1. The study was Conducted in Sweden, a place with "limited sunshine and a low UV index" which would naturally preclude its population having lower vitamin D levels.
2. The study was also lacking in the ability to "distinguish between the consequences of an unhealthy lifestyle and of avoidance of sun exposure"
3. The study had no data on vitamin D supplementation/levels
Why not just tell people to supplement vitamin D instead?
One very consistent pattern with vitamin D research is that association studies will find a major relationship between serum vitamin D and some health outcome.[1] But an RCT using vitamin D supplementation will find no effect.[2]
That strongly suggests that serum vitamin D, at least as we measure it, is merely proxying for something else. The map is not the territory. There's an X-factor that's related to serum vitamin D, but is not just serum vitamin D. Artificial supplementation doesn't work. Since the vast majority of population vitamin D variance is related to sun exposure, that would strongly suggest that sun exposure is the X-factor that improves health.
[1]https://www.cambridge.org/core/journals/proceedings-of-the-n... [2]https://jamanetwork.com/journals/jamacardiology/article-abst...
Just to be clear, I agree with your thought that sun exposure probably carries benefits beyond an increase in serum vitamin D based on anecdotal experience... I supplement vitamin D rigorously, but being in the sun just makes me feel better