Steam is doing well because they made a good platform, not the other way around. Gabe Newell even came out and said that piracy is not a pricing issue, it’s a service issue, which reflects Steam’s approach. They were not even close to being the first online game store.
GOG came well after steam had established itself and, unlike Epic, they are not shitty (they don’t even have DRM at all!) so your argument just doesn’t hold up. Their launcher isn’t as good as Steam but it’s still better than Epic and you don’t even need to use it because, again, no DRM!
Also, let’s not pretend like Epic, a 32 BILLION DOLLAR COMPANY, is some tiny fledgling group: They have, and have always had, more than enough money to make a great launcher but instead they spend their budget on bribing studios with exclusivity deals, trying to bribe potential customers with free games, and of course marketing.
Meanwhile, in addition to making a good, affordable handheld gaming PC, Valve has made massive contributions to Linux gaming, virtual reality, and gaming at large.
In short: Fuck Epic lmao, the entity who is responsible for Epic being shitty is Epic itself.