The solution is simple - create a competitor. Make it competitive.
Epic? They're not investing in the Epic Games Store. It was just a way to short circuit the process. You can tell their lack of investment because features to the store are slow in coming - like they're just putting in minimum effort and minimum dollars to keep it running.
At least GoG is offering a value proposition over Steam and Epic - their games are literally "you own it". GoG can stop selling a game tomorrow, even be forced to delete it off its servers, but download the offline installer and it's yours to play as long as it still runs.
All those game publishers complaining can easily set up a new game store and make it equal to or better than Steam, and people will flock over. But of course, it will take massive amounts of investment to get there.
So the question becomes - will the game companies do the investment it takes? And there I'm not so sure - it's easy to complain about rent seeking and monopolies but to create a worthy competitor takes time and money, and I'm not so sure the game developers are willing to invest their "steam rent" to creating a new competitor, especially since it likely will in the beginning cost a lot more money to run than paying Valve in the near future.
Epic Game Store would require Epic to do way more investment than they are - they only have one trick and it's a free weekly game. It took years to add a wishlist, and years more a shopping cart. It'll likely be 2030 before they have per-game forums like Steam (which are useful to support issues).
And given developers are paying 12% less on Epic than Steam (Steam takes 30%, Epic takes 18%), games are no cheaper on Epic, which really reduces the value proposition to people - if I'm paying the same price, I'd rather get it from GoG first, then Steam, and then Epic.