Yes, Real Debrid (RD) functions as a leech. However, in essence, RD typically only needs to leech once for widely sought-after content, storing it in a cache for quick access by any RD user.
In the worst case, RD may need to acquire less popular content through a few hit-and-run instances. RD actually contributes to minimizing leeching - if each RD user torrented independently on public trackers without seeding, the situation would be more problematic.