I can't help thinking the battle was lost before it even started, no matter how good the offering was because the PC and mobile platforms (where epic operate their store) have 99.9% already decided who owns them. The way I see it Epic wanted to copy what Counter-strike and HL2 was to Steam, but using Fortnite to push their store for a fresh generation of gamers. The problem is they couldn't replace or exist alongside the incumbents while trying to bring in more than a trivial amount of income. The only way I can see the outcome being different is if they were in the position Valve were in around 25 years ago with a fresh or poorly served market or something other than video games, few remember Stardock Desktop as a place they got their games.
They could totally carve their niche if they focused in making their store better.
Could it surpass Steam? Probably not. But you don't need to surpass Steam to have a viable, profitable store. GoG is the alternative that proves the rule - it is smaller, but they have their niche offering.
EGS is shit, and relied on exclusives (which everyone typically hates, especially on PC).
Epic games goes out of their way to be hostile to Linux users. I'm at the point where I just ignore windows only games. And I'm the exact type of person they'd want to convert cause I tell all my friends about my gaming experiences. They could even take proton and use it in their store.