I do not believe without data that switch from one closed source proprietary software provider to another one will guarantee you from hacks.
Switch to open source most certainly does not. Nor is switching from one proprietary provider for your software from Microsoft -> google
That said, it's not the question. The question is if a company wanted to switch away from Microsoft here, what is their option? It's not an inherent statement that one is actually better, but that there is an option if one feels burned by Microsoft here.
Last week Firebase sent me a notification that several of my properties (some of them enterprise apps) had lost domain name verification. The panel in the console was clearly glitched when I inspected it. Two days later they sent a correction saying that this had been a mistake. No big deal, but it goes on to show that Google is not perfect.
Not to mention that GSuite already has 6M different customers/tenants. They're already at a comparable scale, and that doesn't mention that the free versions have the same application security model, with zero incidents (knock on wood). "but scale" feels like it's ignoring the already existing track record and scale and just making excuses for Microsoft.
And that's individual licenses. I can't easily fetch the number of medium to large companies on Microsoft Office vs GSuite but I wouldn't be surprised if it was significantly larger than 50x.
My original contention is that hackers may be particularly interested in that dimension, rather than in the number of individual licenses (which MS also dominates by an order of magnitude).