I mean, I think I get where you're coming from.
I read the "giant particle cannon" as a goofy joke "there's a problem. What's the most nonsensical, simple way to solve it that a person might possibly think of?", and that doesn't read to me as a satire of any socio-political movement or approach. I'm pretty sure no-one advocates the physical destruction of prisons with a cannon as a solution to systemic problems with them. And on a broader scale, I don't see stereotypical leftists, especially "SJWs", as associated with crude, physical and/or violent solutions to problems.
The only left leaning group that's associated with violent, direct action even as a stereotype is the Fox News idea of "Antifa", but I'm pretty sure that stereotype is completely different from the "SJW" stereotype, which I've seen criticised as people focused on talking (ostensibly about minor issues), lack of follow-through and a propensity for pointless outrage.
The thing is, whether those stereotypes reflect reality or not (I don't think they do), they're diametrically opposed to each other. Satirizing SJWs by having a character advocate the use of a cannon is incoherent, because it has nothing to do with the stereotype.
So even if we go full-on "death of the author" and ignore that Jeph clearly seems to be left-leaning and rather sympathetic to progressive causes, so a satire of a broad "SJW" stereotype does not really follow from the text of the comic itself.