This is a classic mis-discussion.I mean are we talking living rooms or stadiums here? There is a pretty big difference in how one approaches the two problems and trust me they are not the same.
I do a lot of pro sound work, but in all honesty, they don't really care about quality. Its all SPL, flying and trucking. And oh yea, if it also sounds good, thats OK too.
I live for small rooms, currently home theaters, where quality in the sound is what its all about. In that space I prefer NOT to have a horn in a region where it does not provide an advantage. In a small room below about 200 Hz. its not about the kind of enclosure, closed, ported, horn, whatever, its about how many. I recently had dinner with a group of home theater specialists and we all agreed that in the very LF domain its all about numbers - at least four, six is better. I have five. And they don't need to be powerful - hell there's five of them! So LF SPL from a single source in any of my small rooms is irrelavent. So much for large horn enclosures.
Now when we can strt to control directivity and the ear/brain combination starts to tell us where the sources and refections are THEN directivity control becomes everything - it controls the sound quality in small rooms at the mid -> HF.
Keep your LF horns, give me six woofers, three monopoles and three ported.