Family sharing required you to download the game when you played it from any other console than the one you own, i.e a friend's. So yes, you would have had to download the 20+ GB game without the disc. The only positive in the scenario was you could begin playing before the download complete. Same goes for installing games from the disc, even after the policy changes iirc.
It's said that they could access your games over the cloud, it did not say that disc-based install wasn't available for them too. The whole benefit of the family sharing was being able to download it, so that was never a problem.
ALSO, I never mentioned family sharing in that comment. I said I wanted to install the game from disc.. for myself. If I pay $60 for a game, I'd like to play it as fast as possible.