You’re right, an Xcode-10 built app run on iOS 13 will use full screen presentations by default. But when I tried that, a grouped table view had a smaller top margin when run on iOS 13 (see the middle of first set of screenshots in the article) so it wasn’t exactly the same. I haven’t tried on later iOS 13 versions, so this might have changed.
Keeping building with Xcode 10 is a short term way to keep getting full screen presentations and not have to force full screen or properly handle the new card-like appearance. Apple have said that all new apps and app updates must be built with Xcode 11 and linked against iOS 13 starting in April 2020.