How much of High End Audio is Horn Speakers?

3-way floor standing speakers with AMTs that are sufficiently engineered to preclude the need to horn load to achieve usable sensitivity.

There are many to choose from. Take your pick. If horns were the answer, then I suppose that Magicos, Rockfords, Bowers and Wilkins, Focals, Raidhos, KEFs, Monitor Audios, Sonus Fabers, Stenheims, Wilsons, MartinLogans, Dalis, TADs, Fink Teams, Cantons, Elacs and the rest of the industry's very best offerings would either be horn loaded designs, or said manufacturers would at least offer a single horn loaded model in their line, wouldn't they?
Horns are best suited for concert venues where sensitivity is crucial to achieve concert worthy SPLs with minimal amplification and extremely long throw coverage.
BTW, I was employed by a pro sound contractor for 14 years and I'm plenty familiar with the concept or horn loading and it's attendant benefits and limitations. I view horns for hi-fi as an anachronism of yore, but there are still those among us who prefer a couple of 4-barrel carburetors over that new-fangled fuel injection stuff, and they are welcome to it.

Each of those brands that you mention has an exotic horn counterpart that sounds different but as good or better.

@vladtheimpala Another example of how different our ears listen, because with my Avantgrade, I have no issues playing at low dbs and getting as good and engaging, if not better, sound as my Wilson Alexx V and  Sonus Faber Aida.

Clearly they all have their own signature, that I like or I would not have bought them, but I tend to listen most of my Classical and Spanish music on the Avantgrade, Jazz and rock on the Wilson and Sonus. 

Yes.  AG's are great "late night, low level listening speakers because the dynamics are still there, even at very low volumes. :)  BH

@vladtheimpala 

There are many to choose from. Take your pick. If horns were the answer, then I suppose that Magicos, Rockfords, Bowers and Wilkins, Focals, Raidhos, KEFs, Monitor Audios, Sonus Fabers, Stenheims, Wilsons, MartinLogan's, Dalis, TADs, 

I have owned Dali, Wilson, and Sonus Faber.  I listened at great length to every speaker you mentioned above and then I heard a horn speaker.  Specifically, AvantGarde horn speakers.  From there, I eventually decided on Viking Acoustic Grande Voix Dual Horn speakers.  I absolutely love the horn sound especially on live albums.  I will never own any other type of speaker except a horn going forward.