As you say, GOG did DRM free when nobody (well, almost nobody) did it.
However, that means that DRM free acted as GOG's USP, and later as its central reputation. As such, no, they could not just have gone without at any time, still hoping to survive against Valve in any sensible way. DRM free was GOG's lifeblood.
With the introduction of its client, GOG has supplied an impressive list of that they'd like to leave eternally optional. It's a great list, it's a commendable list, it's... a naive list. :(
I also agree that the mindset concerning DRM has changed in the industry, yet not in the way you describe it.
DRM has become less of a hassle for customers, hence they've become more accepting, and more of a hassle for content creators, hence they're more willing to abandon it. And as we've all known all along, abandoning DRM doesn't mean less sales for them. However... we have more substitutes, more 'soft'/'social'/'implicit' copy protection/piracy prevention mechanisms than even remotely necessary, from the whole idea of "achievements" to the entire catalog of "pirates miss out" features like day one patches, auto updates, DLC, in game statistics etc.
That's what GOG is doing right now, and I had hoped they wouldn't...
It's not about faith in GOG. It's about the inevitability of the industry standard, naturally with Valve at the helm. :(