Both GOG and Epic stores are quite full of games. Give developers the chance to sell things, and they'll take it.

GOG doesn't have everything since they require DRM-free, but I do most of my indie-game purchases on there. GOG have said in the past that their most-requested feature from developers is "can you make your achievements / social integration just basically exactly the same as Steam, so that it's easier for us to integrate?". Means game updates sometimes take longer to arrive, but hey.

Heroic launcher starts faster than Steam, so I'll grab whatever's free on Epic that week while waiting for it to load; but fuck giving Tim Sweeney any money obviously. Seems to have quite a variety of stuff, tho.

The problem with displacing a company with established network effects is that simply "just as good" isn't enough - you need to be much better to start moving people over. And I'm not really clear what "much better than Steam" looks like. They have great Linux support, great workshop integration, regular sales, the forums are well-regulated, and so on.