Maybe you'd have something approaching a point of Valve didn't:
- charge the standard industry rate
- actually have a pretty easy way of reducing the cut to 80%
- allows the selling of third party keys where Valve gets zero cut
- create the Steam deck, which years on, is still the best price to performance handheld for PC gaming
- actually have basic features like physical gift cards which the Epic store can't even offer because the cut for their store is apparently too low to even allow it
- actively support Linux and proton development to break the Microsoft monopoly
- have a store that is so rich in features and options it makes every single other store in the industry look like a joke
- offer some of the most robust regional pricing in the industry