@unknown slicedlime's videos aren't a source to say whether something is intended or not. When drowneds were added/announced it has clearly been stated that the conversion of drowneds cannot be stopped anymore after 30 seconds. Changing this would break a lot of farms that rely on zombiey turning into drowneds outside of water.
For zombies and husks this is intended. As mojang said, if their head is submerged in water for 30 seconds it starts the conversion process. As soon as this process starts, it cannot be stopped.
@unknown slicedlime's videos aren't a source to say whether something is intended or not. When drowneds were added/announced it has clearly been stated that the conversion of drowneds cannot be stopped anymore after 30 seconds. Changing this would break a lot of farms that rely on zombiey turning into drowneds outside of water.