> if solar radiation was a direct cause of cancer you should reliably see consistent skin cancer rates among people with similar complexion and exposure rates.

...which you do.

> My point is simply that the body is complex, cancer generally develops over years, and trying to narrow down a common link strong enough to claim causation is tricky if not impossible.

That sounds like weasel language to try to muddy the waters to me. If it's tricky or impossible to nail down the effect must be small, and probably not worth caring much about.