That may be true in some cases, but not in all. In particular, the Onion school shooting joke strikes me as a satire of a strawman. Whatever humor can be derived from ridiculing a stupid version of a position (like "school shootings are unavoidable") is, at least for me, made flaccid by the counterproductive nature of the satire. In other words, when the satire ridicules a dumb argument that not many serious people make, it's not so funny.

I don't pretend to be an expert on political satire but I never noticed that steelmanning, to use the modern vernacular, was ever a technique featured in high quality work like Tom Lehrer or George Carlin. I mean, literally never.

It sounds like you're describing something very boring, but if there's a political satirist (or Satanist, or Salafist, or whatever) you think is funny and an exemplar of what you're describing, drop it here.