For the most part I agree.
The problem here is that this kind of system is difficult to make work if your going to impose enough standards to prevent these kinds of problems. To properly "vet" every one of these games coming out of Greenlight or appearing from an indie developer would mean a company like Valve would have to hire dozens of employees just to check the games at the very least. Something which would also fly in the face of Valve's much publicized "nobody has a position" policy since it would involve people very much having a dedicated position and also a lot of power from the perspective of those looking at Valve from the outside since they would be the ones making the decision about what games make it and which ones do not. Not to mention the cost of hiring these full time employees would probably result in increased expenses being passed back to the consumer.
Not to mention the entire issue "bigotry" this kind of thing would create, since when it comes to early access some companies would probably be given a pass, while other less reputable, or just unknown, companies like "Five By Five" (which I had not heard of until now, probably because I don't play shooters) would be treated with a lot more suspicion. Not to mention the issue of newly arising game developers and their economies. That "Unearthed" game seems to be showing up a lot in Jimquisition videos, and while I do not play it, I have to defend it to some extent because it's only charging $5 and if I've heard correctly it's programmed in the third world, not to mention at least having a lot of ambition for a small and inexperienced team. In short it seems to represent exactly the kind of game Greenlight was intended for, allowing a small developer to make back some of their costs as they learn their craft. Something which might sound odd to those who have heard some of my other political posts. Consider also that "Ubisoft" just did "Might and Magic X" for old school RPG fans, which came out early, partially functional, and was taking input from series fans (My Dad got an early access copy, I bought it after release). Many people are doubtlessly going to call it a crappy game, but honestly it's what a lot of fans wanted, and I imagine it will be fairly successful given it's intent. The point being that despite my general dislike of "Ubisoft" they have at least used the early access system as intended and being a big publisher did exactly what they were promising, pretty reliably, "vetting" the system and acting based on reputation and such would probably defeat the purpose by simply giving big publishers like this a pass to release games early access and in unfinished states, under the presumpsion that they can generally be trusted, while effectively picking on the little guys the system was intended to promote. Basically STEAM could handwave "Ubisoft" as we've seen, but would have to take a microscope to the little guys to prevent publishers like "Five By Five" from flooding the market with crap, which makes the system increasingly subjective.
Probably not a well articulated post, but that's my thoughts on the subject.