I really think Valve have become the de-facto owners of the “don’t be evil” motto nowadays, even if they don’t advertise themselves as such.
I have 3 different non-Steam game stores and another 3 or 4 non-Steam game-specific launchers on my PC.
If you're a game dev, small or big it doesn't matter, and your game isn't on Steam, it might as well not exist. The sales and exposure of a game on Steam dwarf all other alternate PC storefronts. Even Ubisoft caved in and released their games on Steam.
Monopoly doesn't mean being the only game in town, you can have 100 other competitors, but if your competitors have <10% market share and you have >90% then you're basically a monopoly.
That's an exaggeration.
World of Warcraft, COD, League of Legends, all exist just fine. For brand new games, The Bazaar is doing very well and they're using their own launcher.
(Slightly off-topic, but The Bazaar is really good, for anyone who likes card-based auto-battler games! Highly recommend.)
What stands out to me is that while most studios accept that they've got to pay their tithe to valve in order to succeed on PC, for many it seems to begrudgingly so and where they have the capability they investigate using their own or alternative channels to get a better rate. It's an interesting parallel to Valve's moan around 15 years or so that Microsoft could E.E.E. PC gaming and the linux direction was hedging against that.