In hit streaming tables, the traffic.source and traffic.medium fields contain values taken directly from the UTM tags in the pagePath (&dr and &dl parameters) for a given hit.
In the session tables based on Google Analytics, the data in the trafficSource.source and trafficSource.medium fields is based on the session data in Google Analytics.
Since the Last Non-Direct Click attribution model is applied by default in Google Analytics reports, direct traffic is ignored, and 100% of the conversion value is attributed to the last non-direct channel that a customer clicked through from before buying or converting. All Direct visits are ignored within 6 months after the non-direct visit.
Thus, it would be incorrect to compare referral data in the session streaming to the data in the hit streaming.