That's a quite extreme view JAR, isn't it?
There's dozens of authors who are objective and cool headed and know how to make the distinction between bad writing and good, publishable quality.
This objectivity helps explain the route of almost all of the people who got published.
Those writers who are objective and cool headed and who know how to tell good writing from bad are in the one percent who get published, not in the group that never manages it.
Really bad writers are bad because they can't distinguish one from the other, at least not with their own writing. . Those who submit really, truly horrible writing simply have no sense at all of how bad their own writing really is. Really bad writing is plain to nearly everyone, except the person who wrote it.
Maybe you have to read a few slush piles to understand just how unbelievably bad most of the writing is. I'd say forty percent of what lands in slush piles is not just bad, it's illiterate. Another forty percent can't be called illiterate, but it's bad enough that it stand no chance at all of even being considered for publication. The bad jumps off the page, and subjectivity simply doesn't come into play.
You really have to get into the top three percent or so before you start seeing writing that shows any real quality, and with it, writers who obviously know the difference, but can't quite manage it themselves.
On the whole, the quality of writing is so bad that all you have to do to make it into the top ten percent is get the grammar and punctuation correct.
Most fiction shows a lack of understanding in every area. The fiction doesn't just have poor writing, it often has no story at all, no real characters, completely unrealistic dialogue, etc. It barely qualifies as fiction.
But the writers submit it with every expectation of selling it. What else can this mean except that those writers have no clue at all about the quality of their own writing?
The sad thing is that this same group of writers are also the ones who frequently mention how much their beta readers loved the story, or how they had the story professionally edited, or who send along dire warnings about what will happen if you steal their stories. They're also the ones to tend to handle rejection poorly, often by sending back the same sort of replies that make most of us laugh.
I don't think consciously trying to judge your own writing is ever a good idea. It can paralyze new writers, stop them from finishing and submitting anything. But an innate understanding is, I think, what separates those who can write well from those who cannot.
Anyway, my real point is that most of the writing in slush piles is not subjectively bad, it's just plain bad by anyone's standards, except those of whoever wrote it. It's objectively horrible.
The whole idea of subjectivity is a trap. When you start thinking it's subjective, you lose any real reason to improve. But good versus bad is not simply opinion. Bad really is bad. Only good versus good is subjective.