You need both. There's many red flags which will only be apparent on a resume (candidate doesn't have work authorization for the country, large unexplained gaps

You need both. There's many red flags which will only be apparent on a resume (candidate doesn't have work authorization for the country, large unexplained gaps in work history, rapid turn-over of employment), plus it's much easier to quickly process large number of resumes, etc. But as you say online presence can often add colour to a candidates profile.