I do not agree that games selling on Steam, no matter the context, is good news for EGS. Clearly the tactic of choosing such a long exclusivity period is in part motivated by the idea that a year later sales will be lower, thus shifting people long term to the EGS and away from Steam. The goal is that at some point EGS can compete with Steam without needing these ridiculous handouts, which especially for indies probably cost easily as much as the production costs of the entire games. For AAA games it's probably enough to pay back the marketing costs, across all platforms, given the rumours of near two-digit millions.
I still believe that at some point this entire EGS thing will just quietly disappear. If a year or two later it's still a giant money sink without turning any profit or sizeable active audience, then even Epic with their Fortnite cash cow will look at better ways of spending their money