The warning is necessary, so I'm not disagreeing with you per se... But I think it's a positive quality of the piece that it doesn't actually resolve to a thesis about the comparison (as might "email is fine, and therefore..."), but just points out the tension. It's up to the reader to use the comparison to take a moment to consider what they think the costs and benefits involved are. Plenty of folks (well, judging from comments sections) think that email fails at many of the things it claims to do, and would assent to an "Everyone sucks here" judgment about both email and the Fediverse.
Half the comments on long blog posts usually end up discussing the headline, or even just part of it. Combine that with the difficulty people on online forums have to recognise blatant satire and you'll end up with pages of discussion about SMTP before you know it.
I see at least four top level comments failing to see the satire or talking about email. The downvotes are pushing them down, but it shows the sarcasm warning was necessary…
I suppose I understand what the author's position is, but they wrote a long post explaining that, since we have a flawed system, we are allowed to create new systems that are as flawed as that one... and that doesn't sound too good