The inevitable decline of Steam is going to be much worse after people spent a decade giving it a free pass on lesser issues.

What specifically are you envisioning? If this is just a general kind of, "the bigger they are, the harder they fall" supposition, I don't think that really holds any water; it's just a platitude. If anything, Steam being so ubiquitous could more easily make it's eventual decline a catalyst for legislation to give software license ownership stronger consumer protections. The idea that we should either condemn it now or stop using it, before its decline, makes no sense to me. Is GOG better? Sure. Can it fully replace Steam? No. Is Steam better than Epic, Origin, UPlay? Absolutely. I'm just not sure what the real point of all this condemnation is when they're by far trying, by and large, to treat consumers well. It's just blaming Valve for not being totally and eternally immune to the effects of Capitalism.

the ‘one good company’

No one claims this. The only thing remotely close to that which people claim is that Valve is uniquely positioned to be one of the best digital games distribution platforms due to its private ownership insulating it against shareholder demands (which is by far the largest driver of enshittification), which is also true for GOG, but obviously Valve is still beating them out in capacity and capability currently.

there are plenty of examples to the contrary

Of course, it's a company. But it's still a billion times better than most of its competitors.