All fair points but I think he quite explicit in saying that that aspect of 'reach' is not relevant to him: he gets an image that is good enough for him irrelevant of whether absolute quality matches the FF gear. And what appeals to him is the options the technology (such as procapture) gives him and the much smaller kit size makes it more flexible.He is promulgating the idea that 300mm is effectively 600mm on FF. It is that for field of view but it is not 600mm on for "reach" unless you are comparing a 20 mpx 4/3 sensor with a 20 mpx FF. You will get exactly the same resolution as a 32 mpx sensor on APS-C. A 375mm telephoto on a 7DII or a 5DSR will give the same resolution as 300mm on the EM1X. I would like the Pro Capture that the Olympus has. A 100-400mm II on a 5DSR has a similar weight to a 300mm f/4 on the EM1X and has the advantage of a full frame sensor, twice the field of view and spot centre focus to be set against the fast frame rate and Pro Capture of the EM1X. Some pros and amateurs would take the Olympus but I far prefer the Canon set up. YMMV.
I have 7D2 with 100-400 and also (recently) the E-M1X with300f4+1.4 tc. Guess which is much smaller. I have only just got the E-M1X so not done full field testing yet but so far it looks promising. Regards reach, both lenses will give 400mm so the bird on the sensor will be independent of sensor size, so the EM-1X gives more pixels on the target. What effect that will have I will be looking at very closely.
I have often said that if you want to talk technical and ultimate quality then talk to an amateur enthusiast. If you want to talk what is 'good enough' without compromising then talk to a professional. I think he exemplifies this.