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.
They got and have maintained that monopoly (I'll let others debate the merits of that wording) by being very very good to their users, which doesn't make the existence of the monopoly evidence that they aren't saints. If they were maintaining it through anticompetitive means, sure, but I've never seen anyone claim that they are, even Epic (who would definitely be making noise if they thought they could get anyone to listen).
The desktop video gaming ecosystem is in perhaps the best shape possible: there's one clear winner at the moment who makes all customers very happy, with a few runners up hedging against that winner becoming abusive after all. If Steam became worse than Epic it wouldn't take long for Epic to overtake them, but as long as it's not worse it's nice that everyone has agreed on a standard platform.
>If they were maintaining it through anticompetitive
Well we know they are now thanks to the lawsuits shedding light in the long known pricing parity clauses. Anyone asking "why isn't this game cheaper on Epic if take take a smaller cut" now has their answer. Without risking any dev's NDA.
For UDK: they did get a lot better with that for UE4/5. These days, the first million dollars in that project's revenue has no cut, and after that it's a 5% royalties (there's also mandatory $1850 subscription seats per year if you have over a million gross revenue a year).
It's about as indie friendly as you can be for such an everpresent tool.