Well you probably can't - that's my point
You claimed that you had:
The burden is not on me to suggest a criteria, since my position is that suggesting a criteria is a necessarily subjective process and so cannot demonstrate that STEM is objectively superior. If you make the claim, the burden is on you to evidence it!
At best, your posts/links demonstrate that STEM performs better on a subjectively selected bunch of criteria that have been subjectively quantified.
For example, I might want to argue that non-STEM is objectively superior to STEM because it makes students better at research. I might cite a study (this is hypothetical btw - I have no idea if such a study exists) that gives graduates from STEM and non-STEM subjects a test that aims to measure their research abilities, and show that non-STEM students significantly outperform STEM students across the board.
But I'd have two problems:
(a) the criterion I have chosen ('better at research'
does not demonstrate 'objective superiority' and I could have chosen any of infinitely many other criteria had I liked
(b) the measure I've used to quantify 'better at research' - the test results - may not really reflect research ability and I can't infer causation from this correlation anyway. Besides, choosing to quantify this way was entirely subjective.
How can I reasonably claim to have demonstrated that non-STEM is superior? I can't. If I'm very careful with my experimental setup, I might be justified in saying that non-STEM is better at producing graduates for research, but that's just one measure. And that's my point: when somebody says 'x is superior', the first question to ask back is 'superior for what?' The statement simply doesn't make sense without this information.
So are non-STEM students superior in some sense?
As do most non-STEM graduates. In fact, if you are correct and STEM really is significantly 'harder', someone who wants better prospects would probably be better off avoiding STEM, doing an 'easy' degree and focusing on the employability skills that graduate hiring teams actually care about. Your degree title and classification is way down their list of priorities - at every stage of recruitment they're gonna be far more interested in your performance on their tests, assessment centres, interviews etc. than in whether you studied Classics or Physics. They're employing you to do a job, not perform calculations in theoretical atrophysics!