I agree with that. Although if there was some way of choosing whether to do homage I think the current flexible system would make more sense. If the kings of England had refused to do homage consistently for their French possessions for a century, and managed to keep the territory, it might well have become what is in game terms de jure England.
It might be quite a neat system actually, if it was balanced so that in most cases both the AI and the player would choose to give homage. The established kingdoms would tend to keep their de jure borders despite de facto control changes, whereas in areas where the king titles are not created, or are easily destroyed, or are held by heathens, they would still drift. By no means perfect, but maybe a little better than either the current system or the pre-patch one.
How to balance it so that homage is given is a problem though. Easy enough for the vassal - a vassal opinion malus, and maybe revolt risk in the territory in question would deal with that. What would be in it for the de jure liege though if it costs him his CB to get the territory back... Maybe if, once homage was given once, there were large penalties for refusing to accept it in the future. And if the land was lost due to inheritance, or the holder acquiring a title that broke him free (Duke of Normandy conquering England), the default position could be homage being given.
Although that does make it a bigger ask in terms of implementation.