When you hold down the delete key in an iOS keyboard it initially deletes one character, then after a delay starts repeatedly deleting characters, and then after a while more starts deleting whole words on repeat. It may even eventually go faster. When you hold down the delete key in a text field in Flutter it doesn't seem to have this behavior.

This may be a very similar root cause to #4818. I have not yet tested on Android, presumably we may have a similar bug there.