Earlier quoted context omitted.
I'm not sure what point you're trying to make here. Of course you can play games without Steam. But I think it is disingenuous to characterize Steam as "just another system to lure users and developers into a Vendor Lock-In" when Valve has seemingly not put any effort whatsoever into locking in anyone despite their unquestioned market dominance.
They recently stopped developers promoting on steam, sale of their game on other platforms. Makes a lot of sense and if the battle with epic games gets worse we might see lock in.. Fortnite changed steam's dominance. Epic games is buying out a lot of games to offer on their store and they have the cash to burn on it. Who knows where all the fortnite fans will be in 5yrs, epic or steam.
Hard to blame them for a stance of "you can't use our storefront to advertise other storefronts" though.
Epic is doing the things it is doing precisely because Steam is so ludicrously dominant. I'd argue that they haven't been successful at usurping that dominance yet. They are still very much playing catch-up.