One major upside for publishers in steam is DRM which epic won't offer.
Sucks that games on Epic don't (yet?) have cloud save/item store/gifting/whatever but Epic can copy if they want to.
I've not kept track, but I'd not be shocked if this was pretty much still the case. It would certainly explain why so many games still have another layer of DRM when sold on steam.
Without DRM your product can just be repackaged and resold, like what happened to the GoG version of Frostpunk being sold on Amazon.
I would have liked some basic version of DRM as well. This will drive a lot of developers to Denuvo, which might be overkill.