Earlier quoted context omitted.
...until it's broken into. I suspect that chances of would-be burglars or identity thieves breaking into Google data are pretty slim, in comparison to a home-installed system. OTOH both Google and a private person can be strong-armed by a court order, or even a three-letter agency, to open up their AI knowledge vaults.
The difference is one of targeting. It's like saying "People would never break into a bank, when they could break into someone's house and steal their stuff" It may be easier to break into someone's home-brew system, but generally it would be unlikely to happen unless you were being otherwise targetted. Whereas google has a lot of users data, which could make it a more attractive target.
If you're a "person of interest", you'll be attacked either way.
If you're just a regular person, like me, you won't likely be targeted. But my chances of getting a collateral damage are much higher in a centralized system: when it's broken into, my data have a chance of being siphoned off along with data of someone less ordinary, who was the target of the attack.