It was stupid mistakes that led to takedowns of Silk Road, KickassTorrents, The Love Zone, Sheep Marketplace, AlphaBay, and Sabu de LulzSec.
However, Operation Onymous did rely on Tor deanonymization data provided by CMU researchers to the FBI. The CMU group had exploited a bug in Tor to get ISP-assigned IPs for numerous users and onion servers.
Even so, Operation Onymous would arguably have failed if those users and onion servers had accessed Tor through nested chains of at least three VPN services. And used firewall rules, and isolated VPN and Tor gateways in separate machines/VMs. Isolated from workspace machines/VMs. Also, operators and users of those onion servers would have remained safe if they had done the same.
In a few other cases, such as Freedom Hosting and Playpen, the FBI used NIT malware to deanonymize users of onion sites that had already been confiscated. The malware bypassed Tor to send IPs and other information to FBI servers. But only Windows users were affected, because the NIT only ran on Windows. Also, users that used firewall rules and/or separate Tor gateway machines (such as Whonix) were unaffected. And finally, even Tor browser users would have remained safe if they had accessed Tor through nested chains of at least three VPN services.
So yes, use nested chains of at least three VPN services to access Tor. And watch your OPSEC. Compartmentalize, compartmentalize, compartmentalize!
So, the approach is insufficient only if you're sloppy.