He's actually more of a social observation: it doesn't matter what the technology can do, what matters how how the developers of that technology actually use it.
People who use PDF almost never use 3D graphics and heavy dynamic JS, so PDFs almost always have many of the qualities he's seeking.
Web developers almost never inline anything, and do all kinds of things that are arguably deal-breakers except for a few lowest-common-denominator use cases.
> Under the hood it seems apparent to me that the real premise is an emotional one, not a technical one.
The premise is that the web has failed in important and clear ways, it's impossible to fix so we should give up, so many use cases should abandon it for something else, and PDFs are unexpectedly well suited for that.
On a related note, part of me wishes Java Applets never died. Getting rid of them seems to have caused the Web to turn into them, and maybe if they'd remained some kind of separation could have been maintained.