
Is the problem simply that you couldn't buy the game from your preferred launcher? You can easily add a non-steam game to steam and get steam inputs in most cases, I played all of Stardew Valley from GOG and Mass Effect Andromeda on EA Origin through steam with my steam controller.

What does it matter if Epic paid for exclusives? The studios or publishers deemed it financially beneficial to get an immediate return on their game, and an exclusive period that nearly every studio that took the deals said amounted to an Early Access release before the "real" release 6-12 months later on steam.
