You’d be surprised how easily you can export pretty much all your Apple-app data using AppleScript on a Mac. There’s almost nothing inaccessible via apps’ APIs
I keep all my personal stuff like email, messaging, browsing on Mac where privacy is higher and easier to maintain.
I do all my dev on Windows for the most part, along with my corporate Outlook account (which I use in a tab in Chrome, not even installed on Win10), that's basically how I do things.
This also allows me to make snapshots of Win10 whenever I'm considering installing something that might f-up my machine (aka test out some alpha release of dotnet core etc).
Sure, he might be able to export his data but what use is that??