Like I've said several times in the past, back when LE and Pep was the coach, Barca had a top class backline and Xavi and Iniesta in their prime. Not to mention hardworking, pressing wingers while Messi was able to be lazy as false 9 at the time.
Busquets always had the same severe vulnerabilities, they were just masked by the WC players around him. As Xavi and Iniesta got older and left, as well as a decrease in the quality of the defense, it got to the point where his vulnerabilities became a clear liability.
A liability that all top teams have exposed since. You dont need to really understand football to see it either. It's quite clear he's caught out of position many times, which he has always lacked the speed to compensate for it, and they've counter attacked us starting through the middle regularly.
Why do you think when De Jong isnt playing and babysitting him our midfield looks disorganized and disjointed?
Busquets was a good player who thrived at Barca because it was the ONLY system he could of ever thrived in. Once some of the pieces werent there, he became average and has been exposed since.