well......when they make a horn or panel that are truly full range and seamless top to bottom (and I mean really frikken seamless at warp 9) then we can consider those approaches. but so far you have to listen 'around' the compromises (dsp?) to consider them.
or 'settle' for where they are really good.
no offense intended.
Truly full range and seamless top to bottom is not a function of cones or panel or horn or the technology used. Ill take for example your MM7... Cone at the bottom , i think some treated
papermaterial ... Acuton (Ceramic) drivers for most of the rest and an Aluminum ribbon on top. Yet this assembly of, excuse the choice of words, disparate material and technologies is to you and most who have heard it, an immensely satisfying, accurate and seamless top to bottom transducer. It is proof of what can be accomplished with any technology and refute violently your position. Let's call the approach hybrid for the lack of a better term. Hybrids can work.
The notion too often branded with an air of irrefutability that only horn subs would work with horn or a variation that only the subs made by the manufacturer can truly work with a given speaker or that only ESL can coherent, etc are as false as it can be and are regularly proven wrong by countless of serious systems of the highest caliber.
The reality of life and there I have to beg forgiveness for the use of a truism is about compromises and speakers are full of those by their very nature. The ideal would be one driver who would reproduce the entire range Virtually impossible with cones (Hell yeah! 100 to 10 Khz is not full range), fraught with issues with ESL (Most are not full range or if they have to be it is several panels assembled in some forms not just one) or they are severely restricted in output or ...same with most panels and I know of no full range compression driver; it is always multiple ways with horns. with the lowest notes requiring gargantuan horns .. 20 Hz in horn requires things that would be more than 10 meter long .. so people do basshorns that have to be equalized substantially to be of manageable size or have to build the basshorn into their houses... So we all end up with compromises.. Multi-way speakers are compromised and their crossovers are, analog speaker level crossover are very, so very compromised it is a wonder they work at all.
Taken on their own horns and their variants the waveguides offer mostly advantages. One of them being a better coupling of the transducer with the medium (the air to your ears), something we all want and that only horns and waveguide can offer. They also offer the promises of controlling
mechanically the directivity at various frequencies and I would say that it s;lowly downing to me that directivity is one of the most important aspect in the way speakers react in a room... the final determinant of the sound we hear. Of course some of them not properly executed present distortions that are obvious, the honking for example. I see many celebrated horns with the drivers so widely spaced that it is a wonder that they can ever coincide even if you were seating in a neighboring country, thus you often hear that horns do not image well. That is not the case for those that are properly executed. As a matter of fact the better horns imaging say the JBL are something to behold. I would also take exception a the audiophile tendency to equate this with a price range . I cringe when I see things like you need to go north of 100 K to get what horns can do. No! WHile there is the tendency to bow at the altar of price, great results are achieved when people take their time to optimize their systems: it takes a while , takes knowledge, takes patience and humility. The humility factor shouldn't be forgotten: While it is about the sound we like we may have to remember that music often conveys a message and this is painstakingly clear in the choice of instruments from the people who brought the music. the screeching ( oh yes they screech) of violins has purpose... a system that makes a violin sounds sweet, a sound so many love is not doing justice to the music, is not carrying the message. of course the owner has all the rights to like what he/she likes but ... it would be more fulfilling methink to hear what Beethoven or Dvorak or Penderecki or (plug your favorite composer/artist here) had in mind .. were trying to convey.
So it is possible to have top to bottom coherence, great imaging and accurate sound from almost any technology. In the here and now, however Horns can do all of this plus a level of dynamics reproduction no other technology can even hint at. That is why I like horns. And it doesn't have to cost an arm and a leg. And it is better to mate them down low with properly DSP'd
cone woofers. My dream is JBL K2 (or M2) with 3 Infinite Baffle subwoofer ( with at least 2 x 18 inches drivers) : 2 IB in the front of the listening position and 1 the back. DSP'd, EQ'd and time aligned with the mains.