Exclusive games are definitely desirable. If they get those, then the rest will follow, and they will have some games that aren’t exclusive, but are still sold there, occasionally dropping in some cash. They’ll also still make licensing revenue.
What will also help, again, is if they really pump that content creator\influencer program (in association with devs). The conversion when a streamer posts a “buy” link is actually surprisingly high. If the buy link is associated with the Epic Store, and a gamer doesn’t give a shit that it’s not Steam (which many of the younger ones will not), then they’ll get those purchases.