I have built plenty of 2-ways with discrete drivers that play louder and cleaner, image superbly, and provide excellent frequency response down to at least the same point - and also need subwoofers to plumb the depths. Coaxials are IMO just an over-hyped technology that costs more to get decent performance from - and I don't see that price point dropping. Others are in fact jumping on the same over-hyped train because they can sell coaxial speakers for a higher price, not because they are looking to compete with a lower price point product. It's just more snake oil to shake more money out of gullible buyers hearing false advertising copy about better imaging, coherence, etc. As I have said before, coaxials don't do anything better than discrete driver loudspeakers. As I have also said, good 2-ways free you up of the need for a crossover in the most critical 150 Hertz to 800 Hertz region, and they can be built easier and cheaper than coaxials...
This is like the (I just lost count) post in a row where you only tell us your personal/subjective opinion on coaxials. We get you mate, you are not very fond for them, but you haven't enlighten us yet nor provided any actual data to back up your claims, with the exception of your (very personal) "150Hz to 800Hz crossover rule". ¿Is it really 150Hz to 800Hz region the most critical? ¿Who says so? ¿Has it been proven?¿Why that region and not 1kHz to 3kHz, just to put a different example?.
I also don't get why you steered all your claims based on only small 2-ways Uni-Q config. ¿Are those old or contemporary speakers? ¿Why not specify models? OP enquiry about coaxial technology regardless of configuration.
The same is true for your recommended 2 way discrete drivers...no model, no data performance, no nothing, just your thoughts...and not really sure what you mean with discrete drivers clasification...coaxials are also discrete drivers, a midrange and a tweeter, but sharing a concentric configuration over the coil axis.
Coaxials being "extremely power limited" ?????? Unless we are talking about an active design, I haven't seen any power limitations on all the passive coaxials tested by Amir and Erin.
In fact Erin thoroughly measured different isolated Uni-Q drivers several years ago, prior to start testing speakers with Klippel NFS, and the results doesn't show any pinch of power compression. At the end of the day the midrange will behave like any non coax driver, it has its own motor magnet and not affected by all by the tweeter in that regard.
Vertical directivity isn't actually all that critical when you're seated in the hot seat listening to two speaker stereo music, unless you suddenly get up from your seat to stand up. There are quite more than "a few examples" of loudspeakers with discrete drivers that deliver pinpoint imaging. I for one have owned many, including ones I have designed and built.
Except there is little evidence that time alignment and perfect step response is even critical. Our auditory system only processes timing information over a narrow frequency window, primarily 200Hz - 1Khz, rapidly declining after that. That is likely why time alignment and step response has not correlated well to listener preference.
We should first clarify that there isn't a real consensus or definition among most listeners and members about things like "pinpoint imaging", "soundstage", etc. It is quite a subjective terminology, and much harder to quantify like tonal balance for example.
In the absence of such a consensus or standardization, I refrain from data that could provide an answer to this difference whereby many users feel they get "pinpoint imaging" with coaxial. Therefore, the fact that the drivers have the same acoustic center, are aligned in time, and have a better step response, as well as excellent directivity, is one of the few data we have that can explain the difference with other topologies.
Now what I don't understand is why leave aside the vertical directivity? It is true that 95% of the time my listening sessions are sitting on LP, but when I get up and walk around the room, it is incredible how the response is not modified, and this is a simple demonstration of the pedigree of this typology. Back to the objective, a good vertical directivity will cause better interaction of the reflections with the floor and ceiling, a better Total Early Reflections response, therefore a better response in general, all this also affects when you are sitting on the "hot seat"...
It makes no sense at all to limit yourself to prioritize only the horizontal plane. Under that same logic, I could say that multichannel reproduction is not so critical, stereo is not so critical either, let's listen in mono, and in fact, it is not even critical to use several drivers, so a single full-range cone is enough, why worry about the cabinet if a cube box does the job, you know what? A single Auratone 5C in mono is enough for everyone (irony).