Of course they could always add something like PIN/QR code/plugging the iPad into the MacBook for local connections - but that will never happen with an Apple that prioritizes simplicity over functionality.
I mean I don't know why people get so upset about this sort of thing. People who own two recent model apple devices and want to use them together like this definitely have iCloud accounts and are signed in to them. I don't know why someone who doesn't want to use apple services would have the hardware.