He makes a good point about Barca having defensive deficiencies. But once again, I think it gets back to missing Messi. Without him, Barca can't get in their preferred attacking shape/mode - high and narrow.
As great as Messi is with the ball at his feet, I think the thing that really sets him apart is his ability to creatively find and use space without the ball. It's like he just sees space and motion differently than everyone else. And that allows Barca to do the high/narrow thing.
So back to defending; when Barca are doing the high/narrow thing, when they give the ball away they're already so compact that they can quickly get numbers around the ball. They either win it back quickly, or suppress the other team's ability to quickly counter by putting immediate pressure on the ball. Without Messi, Barca's offensive shape isn't as tight and therefore opponents have space to operate on change of possession. And when that happens, the individual defending weakness becomes apparent.