As an anecdote, the websites did seem to load slow for me. And as a previous commenter has added, I'm not sure a news hub is best suited as a SPA.
The article itself is all fluff and big claims with very little info about what's novel here. I'd expect better from a news org.
It's certainly highly debatable as to whether there is any genuine benefit in presenting a text-heavy (in theory) site as a SPA. Bloomberg does the moderately clever "one article follows another article" thing, which I personally quite like but others here were fairly negative about.
It seems most sites that have speed/responsiveness/usability problems, get those problems mostly from their ads. It doesn't reflect well on the site or on the ad. I suspect it's because the metrics ad networks are using don't capture their crappy performance. I wish the original sites themselves would track ad problems and thus drive SLA compliance.