I don't think not buying a game like Operencia has anything to do with principles or being a "Gaben slut" for an average gamer. It's just that whatever window of opportunity these games had (assuming they ever had any) is long gone now.
It will absolutely be interesting to see how it effects sales, sure. Ashen supposedly sold poorly on Steam and GOG a year later, but is that because most people who were interested got it on Epic, or that because a year of exclusivity away from the biggest platform by far made it less interesting? I hope more sales numbers come out that shed light on that. For example, a game that was a bomb on Epic but sells very well on Steam would say a lot about Steam's market power.