It is worse, even less than useless. With the California case, there is very little go gain by lying and not putting a sticker on items that should have one. With AI generated content, as the models get to the point we can't tell anymore if it is fake, there are plenty of reasons to pass off a fake as real, and conditioning people to expect an AI warning will make them more likely to fall for content that ignores this law and doesn't label itself.