i have had good well respected horn speakers, and also heard some very very tip top horn systemsApparently not the tippy top yet, or something to that effect :)
Many systems can be shouty; this is caused by distortion. You don't need horns for that, just poor setup.
The mark of any good system is you can't tell how loud its playing. It should never sound 'loud'. To that end horns really don't have anything more or less to do with it except that its easier to do with horns since amplifier distortion plays an enormous role in making this work.

