I think the mic issue is a negligible one, relative to what other experts such as the respected Guru, Dr. Toole who cited some "reasons" in one of his book, titled Sound reproduction: loudspeakers and rooms
To get a fuller picture, one would have to read the whole book, but for now you could jump to page 518 and note what he said about measuring the room at above 200-300 Hz.
"If the room is rectangular, and multiple subwoofers are arranged in certain manners, as discussed in Figure 22.4, then a special kind of equalization occurs: spatial equalization, wherein multiple listeners can get to hear similar bass. Then the normal spectral equalization can be added to make that bass good. This is the “icing on the cake.” A high-technology solution exists for nonrectangular rooms or other difficult situations (see Figures 13.18 and 13.19). The situation is very different at frequencies above the transition frequency of about 200–300 Hz. The loudspeaker itself takes on most of the responsibility for what we hear, but the room remains a factor in what we measure—and that is the problem described in Figure 19.1. Steady-state measurements—room curves—made at the listening position are not reliable indicators of very much except at low frequencies. In these measurements, a microphone collects sounds from all directions and at all times following the direct sound, adds them together, and presents them to an analyzer, traditionally a 1/3-octave analyzer. The notion that this simple process can reliably predict what is perceived by two ears and a brain is preposterous. Using this information as a basis for equalization at middle and high frequencies compounds the error. Some elaborate equalizers make time-windowed measurements attempting to separate the direct and subsequent reflected sounds. This is a thoughtful move in the right direction, but the measurements are blind to direction: they have no idea where the sound is coming from, but the ear-brain system does. It also sacrifices frequency resolution to see into events in the time domain, meaning that the more precisely the sounds are separated in time, the less information we have about them (similar to what is shown in Figure 13.23). If we had detailed measurements on the loudspeakers to begin with, much of this would be unnecessary. Equalization can change frequency response—that is all. As can be seen in much data shown in Chapter 18, loudspeakers can have many problems that are not revealed in room curves, and they can have directivity problems that can show up in room curves but that equalization cannot address (Figure 18.10). The only cure for a loudspeaker with directivity issues is to take it back to the engineers and tell them to redesign it. The complex sound fi eld in rooms can add other aberrations that the human perceptual system takes in stride, meaning that if one starts with truly excellent loudspeakers, equalization based on in-room measurements has a chance to degrade them. As stated earlier, we need to have detailed and accurate information on loudspeakers. Then and only then can we assess what the loudspeaker is doing and what the room is doing to it. Room curves bundle all of the information together. At middle and high frequencies, we learn more from an analysis of the loudspeaker than we can learn from room curves, even though both are helpful. It is time that comprehensive anechoic data on loudspeakers was widely available. Ask for it....................."
So while the issue is more complicated, it does seem to me from the above, that one of the issues was about the measurements above the transition frequency being not reliable, as he explained elsewhere in this book and his other articles/books. The book was from 2009, may be that's why it is now downloadable. I am not sure if he has updated this part in the latest version, now that we have updated REQ systems such as the popular and more affordable Dirac Live, and XT32 widely available, and I would think that with their much improved resolution, they must be doing better than Dr. Toole's cited 1/3- octave analyzer.
Here's another article he wrote, see page 4 where he also touched on the related issues.
Maximizing Loudspeaker Performance in Rooms (cieri.net)