A coaster does not attract any new guests to Epic they don't already have. Universal fans, who like coasters, are already a captured market.
The growth market for Universal/Epic is Disney guests not already going to Universal parks because they associate Universal parks as screen-heavy or coaster-heavy, and lacking family-friendly thematic, vibe-filled attractions (Pirates, Haunted Mansion, Jungle Cruise, Fantasyland, etc., etc....). With a few more of these per park, Universal has the opportunity to drain off some of the guests from Disney resort. These tourists who already like theme parks -- generally -- and go to Orlando are such easier guests to attract than someone in their living room in Kansas who doesn't already participate.