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.
I mean, I'm pretty pro-steam myself but competition is always a good thing for consumers. There are plenty of features that Steam users have been asking for for years and maybe another competitor in the desktop marketplace can light a fire under them, so to speak.
That's the whole problem, Epic hasn't approached the situation with the intention of being good faith competition. They have instead attempted to exclude competition by paying for platform exclusivity. That's anti-consumer. As a consumer that annoys me. GOG is competition for Steam, they offer a genuine value via DRM free versions of the same games ALSO available on Steam. That leaves the choice in the buyers hands as to which platform offers a better value. It's a big difference in my opinion.
Steam's maintenance downtime (as someone on US Eastern time) and just general glitchiness has been a bit irritating lately. I wouldn't mind some competition but Epic isn't a Linux friendly company so ... I'm not exactly rooting for them.
However, I'd like them to poke Steam just enough that Valve reduces their downtime to almost zero.