Unlike Apple and Google, Valve isn't blocking other digital distribution platforms on PCs, nor do they control the operating system, so that's not really comparable. Microsoft isn't either, for that matter.
What Epic really wants here, is not to just cut Apple and Google out of the large cut they take for selling virtual goods in their games, but to get their own competing app store on those platforms. They ultimately want an Epic Game Store for mobile devices where Apple or Google isn't taking a 30% cut of all sales on the platform. On PC, they can do that, but on mobile devices, Apple and Google tend to have things locked down to prevent that, or at least make it more difficult.