Horn based loudspeakers why the controversy?

Kosst  it's all a matter of mathematics. Thanks it in these terms. You have a speaker that is 100 db efficient.  The source music goes from 10 DB to 30DB.  You multiply the two numbers together to get your final levels.  You are going from 1000 to 3000. Now take the efficiency of the speaker and substitute in a figure of 80db efficiency.  The source music still goes from 10 to 30. Do your multiplication and you get 80 to 240.  In the second scenario spread is much smaller than the first scenario.  That represents the dynamic range.Obviously this is a huge oversimplification  as the decible scale is logarithmic, but I think it serves to illustrate what I'm talking about. Increasing the power of the amplifier which can bring you to the same peak  levels will not give you nearly the same range. People continue to confuse dynamic range with ability to play loud and they are two different things. 
 So if you call continuing to try to correct misinformation not taking no for an answer, I am guilty as charged. 
Kosst  about 5 to 10 years ago I used to think just like you. I thought all vintage stuff must have been massively superseded by today's offerings.  I believed the magazines with all their reviews and advertising drivel.   Then I met a few friends who were older than me and had been into Audio since they were in their teens. They'd collectively pretty much owned everything at some point or another,  The one guy had made a lot of money flipping gear just prior to the Internet and in the beginning years of the Internet.   At one of their houses I heard Vitavox horns with SET amplification.  That's basically gear who's technology predates  the stereo era.  Granted it was set up with a top-of-the-line clear Audio table and Goldfinger cartridge.  Upon hearing that I realized that the best today's mega dollar offerings can hope for is to approach equalling it. In fact all of today's mega dollar offerings I've ever heard did not even come close, but I'm giving it the benefit of the doubt because I haven't heard all of it.  
The other funny thing is that with all of their collective experience, none of these gentleman ever, ever, ever participate in forums anymore.   In fact the one gentleman was a leading expert in the electronics and telecommunications fields for 30 years.   He holds numerous patents in his name. He has scratch built his whole system and it too is better than any modern commercial offerings I've ever heard. When I asked why, they explained that because when they try to correct the miss information they basically get shouted down and treated like idiots. I totally see what they mean. 

@analogluvr 
Yeah, I'd say it is an oversimplification. It takes into no account gain of an amp. The kinds of dynamic compression you're talking about would be glaringly apparent, but the reality doesn't seem to reflect that. 
The funny thing about all this is that I was a real stalwart for years expounding on the virtues of old gear. I never had a warehouse sized listening room like some of you seem to have for these massive horn rigs, and I never wasted my time with them. I've still got a pair of ESS AMT1's. If you can tolerate nondescript bass and a hollow midrange, they're awesome sounding speakers, but they're nowhere near as convincing or uniformally flat across their power band. 
The sensation I've always gotten, even from the best horns I've ever heard, is the same sensation I get standing right in front of a trumpet or sax horn. My dad and brother played trumpet. I played sax and electric bass. It's no mystery to me at all why you NEVER see horn loaded bass guitar rigs. The very last pair of horns I heard were these big JBL SOB's at Pine Knob. I HATED them. They were a perfect example of large, honky, in-your-face, broadband horns. And when I say "in-your-face", I mean even from 75 feet away they felt like they were drilling the sound through you from a totally nondescript point which was anywhere but the stage. The friend that came with me even commented on how honky and distorted the sound was and he really doesn't know enough about audio to have a prior opinion.
I'll say it again... If somebody has a pair of fully horn loaded speakers that take up 3 square feet each, bring them on over and prove me wrong. 

@whart 

Have you used your Quads with the ML2?

I'm really enjoying the Klipsch Cornwall III.  Rated at 102db efficiency.  I've added a Fostex horn super tweeter to extend the upper frequencies.  The super tweeter sits on a Symposium Svelt shelf which also addresses some midrange resonant frequencies on the cabinet.  The speakers sit on top of a pair of Rollerblock 2+ double-stacked which brings everything into focus and cleans up the low end.

http://assets.klipsch.com/product-specsheets/Cornwall-III-Spec-Sheet-v03.pdf

A real sleeper in today's market.

One thing I do not particularly like (not that I hate it, but I find it swaying me not to buy) about most modern horn speakers is that the horns are so often made of some kind of plastic but that there is generally no attempt by the manufacturer whatsoever to damp them on the rear side. If you were to walk up to such a horn (the larger the horn the worse the effect) and flick it firmly with your fingernail then you’d instantly get a very good idea of what the horns are actually doing to the sound. I suspect most people are under the impression that the vowel characteristics that are often associated with horns are somehow coming from the shape of the curve or their dimensions, but I don’t think it’s so. I find it most often due to simply being that the horns typically go undamped in most designs.

The real rub for me here is that the reasoning that this effect can and should be dealt with in other aspects of design (crossover design, EQ, placement, or whatever) Completely misses the point. Properly, the vowel sound should be dialed out of the equation as much as possible from the start. You damp it out physically - no more vowel sound, no more problem, right? We don’t as a rule tolerate vowel sounds in box designs, in fact makers regularly go to great lengths to tout that they’ve removed them with careful attention to the cabinets, don’t they? So why are so many makers of horn speakers so seemingly silent on the subject of audible horn resonances - especially as it relates to horn material?

Just my 2 cents though.