most of what you said is not correct, especially technically. That a studio speaker sounds fatiguing is correct, but only under certain circumstances and technically for different reasons than you described above.
First, such speakers are build, as said in my posts above, to have a very controlled on/off axis directivity, alot do by using waveguides or via d'ap design for vertical controll, wave guides also to match the treble and upper mid range towards the midrange/bass driver directivity/bundelig of the sound, e.g. like in a two way speaker. That way the off axis frequency response is controlled and balanced over the frequency response and x-over point, which some consider far more important than some linear or non linear distortions. The ear is very sensible to off axis colorations in the treble and mid range, where in the bass range smaller distortions are often not noticed. So via their controlled directivity of sound, much more direct sound will hit your ears. This ultimative effect cannot be met to any listening distance or any seat, as then the physical design of that speaker would bring it's own negative side effects (huge horns = colorations or micro reflections). Also in studios far field most often ends at 3 to 5 meters (9 to 15'). And usual listening distances of smaller monitors then "main monitors" are much shorter, like 1,5 to 1,8 meters (1 feet = 0,33 meters). When you listen for example to a Genelec 8050 within spec, one of the most sophisticated and engineered two channel speakers, speced for a listening distance up to 2,3 meters or 7 feet only, the sound picture becomes immidiately bright. That is because you get alot of direct sound, not becaue of cone material
. If you would sit further away more reflected sound kicks in, which will darken and overlay the sound picture. The quality of the room will be decisive. You loose sonic resolution of the input signal.
High end speakers are known for their bad directivity and at very high listening distances, it is no wonder why they sound so "round" (plus point two described below).......that has nothing to with precision or real resolution of the input signal anymore. We talk here more about the art of flavor, not about he faithful reproduction of the input signal.
But secondly, there is one more point, that is frequency response as such. Some of these monitors will almost draw a straight line when measured anachoic or free field. That is not true at all for high end audio gear, so it should be clear now why such measurements are missing on the websides of such high end brands. It's also clear why you miss midrange in studio gear (talking best two way or main monitors), because there is no enhanced spectrum at all. There is no sounding taken place. These speakers do not try to impress you. The imput signal should
Third the room. How many that claim the fatiguing have listened to pro gear in optimized rooms ? Pros do only, because there is a (philosophy and direct) relationship between the two, and I bet alot of prejudism comes from taking a pair of 2 way Genelecs into a living room and then wondering at 10 or 11 feet why it sounds the way it sounds
The best pro speakers will have such controlled drivers via a 3 way or 4 way full active tri or quad amped designs, that by increasing volume, the full spectrum is increased in loudness respectively, until you get a clean plop noise of the bass or mid range driver hitting controlled the displacement limit of the driver (often the limiter will prevent such an event). You will reach a point where in a poor room the treble will become unpleasent, although just plain increased linear, where a poor passive speaker will show non linear behaviors or compression. The pro monitor is not guilty at all, it just did it's job linear at any given volume. So the room must follow, then the picture turns around.
I think this discussion cannot be won from any side. In the end the client will decide, and the request for brand name as well. Who wants to spend more money than necessary should. It's a free world for budget and taste.
However, and that is the only remark I actually tried to make. With such sophisticated installations Peter is planning, is does not matter what high end brand he is hiding in the corner closet, it will not make the main difference and it can never be the best, maybe only the world's best compromise for 10 to 20 seats.
One more remark on pro gear and treble. If we say pro gear will not try to add a character to the sound, just play back the input signal, then it implies they all pro monitors sound the same. That is of course not true. Using different filter slopes, different driver layouts, some with d'ap, some with waveguides, some with dsp correction, they will do sound differently. Overall, the goal is the same, and the best of them get in sound closer to each other, the approaches just differ, hence the results differ.