I haven't read Piketty, but Google Books allowed me to read a few pages to make sure that quote wasn't taken out of context. So I agree that "None of this is false," but I question the value of measuring welfare by asking what percentage of the total someone holds, rather than more direct measures of life quality, like food, shelter, and health. I also agree that wealth naturally accumulates unless checked by policy. That is precisely why "The target of reducing extreme poverty rates by half was met five years ahead of the 2015 deadline."
You should read Piketty. He wasn't measuring welfare by any stretch of the imagination - he was measuring capital flows and the function of owned capital in wealth generation. Fact of the matter is, he basically points to the massive redistribution of wealth during WWII as the engine driving the post-war economic expansion without once saying the words "jew" "holocaust" "crystallnacht" or "ghetto"; I'm guessing because it would have opened up exactly this sort of bullshit argument. More than that, "extreme poverty" isn't even vaguely a focus of the work. It's entirely about the top two deciles and how they compare to the middle six deciles historically and why. He even burns a few pages about how historically, the poor aren't even counted so it's difficult to find any metrics about them. He focuses on the middle class and the wealthy because that's where the data is. Yet in your linked article, it forms the justification for some dude in a suit to go "look - it's not so bad as it was during the dust bowl." NO SHIT. How offensive is that? "Could be worse, you could have cholera." Fuckin' A - if we're taking "a reasonable expectation that the advances of modern science will raise the quality of life for all participants in society" off the table I'ma start gettin' strident.
Here's a nice graph of that data. https://ourworldindata.org/grapher/declining-global-poverty-share-1820-2015