I also didn’t find it to be informative at all. They seem to be ascribing a cause (on very dubious data) to the wrong things – they focus on lazy loading and other recent features, but the real story is the continual downwards slope across 20 versions… What’s that about? The only conclusion you could reasonably draw from this extremely limited data is that WordPress is getting inherently less performant over time. I can’t imagine that’s the case. So, there’s something else going on.

Is there a way to measure the total “load” for these sites? Are newer sites simply using more media, plugins, features, interactivity etc…?

What hosting are they all on? A defunct text-based blog on 3.5 will run well on even the worst shared hosting. But a “modern” site with ecommerce, social networking etc… will struggling even on many of the most popular VPS providers.

Is there caching? CDN? etc…

There’s surely a dozen other questions that could be asked with minimal scrutiny. If it isn’t possible to get the data to at least attempt to answer them, then perhaps publishing a “study” like this should never have happened…

As such, its not particularly encouraging that this all seems to have evaded the people who are tasked with improving the performance of WP…