I agree, But then it can't be said that it adds 'leading edge information' when clearly it will only make the situation objectively worse. And you can't time align a driver which is more than 1/4 wavelengths away from the other.
If you want to add a super tweeter onto a badly designed speaker then yes it will add hf in a haphazard way, but it's not going to sound as good as just getting a good Tweeter with the top end extension you want.