The documentation is not updated but both appear the same to me, just different default sizes, and perhaps you can't change the size of pageSheet via preferredContentSize?
On iPhone, form sheet and page sheet look identical and on iOS 13 use the new card-like presentation (where the presented view controller doesn't quite fill the screen and the presenting view controller is still slightly visible behind it).
On iPad, form sheets seem to behave on iOS 13 like they always did: they appear at a fixed size. Page sheets, however, now appear at a different size than before, and that size varies according to the Dynamic Text size configuration (larger sizes makes the page sheet bigger to accommodate a larger readable content guide).
I wrote an article on Medium which goes into a lot of detail on the iOS 13 view controller presentation changes: https://medium.com/@hacknicity/view-controller-presentation-changes-in-ios-13-ac8c901ebc4e