First: Mirrorless is an evolution, not a revolution.
Third: Think Olympus and Panasonic. Sony is late into the game, same as Canon and Nikon.
I see it differently.
A. Sony was the first one to make mirrorfree cameras for real, both with APS-C and even more so with FF sensors - cameras and lenses that can more challenge any mirrorslapper system head on.
B. Quarter-sensored retro-styled gear does not fully count. That's why Olympus and Panasonic [consumer gear] along with all of mFT universe are doomed, despite having been first with mirrorfree cameras.
C. If mirrorfree was only a "tiny evolutionary step" then CaNikon would not have withheld that technology so long from their paying customers. Mirrorfree is a paradigm shift, both for users and even more so for oligopolist customer-milking corporations like Canon and Nikon.
In reality, mirrorfree camera gear [with global shutter sensors] really is "stage 2" in the 3-stage transition process of 19/20th century photography gear into 21st century:
1. Film -> Digital - chemistry stuff
2. Mirroslap -> Mirror- and Shutter-free - eliminate moving mechanical parts from cameras
[step 2B is removal of mech iris blades in lenses, pelaced with electronic "LCD"-screens with variable size, always perfectly round openings]
3. Single, large optical lenses -> small, multiple lenses/computational photography = elimination of large, expensive polished glass lenses from photography
That's whats really going on and what really upsets CaNikon's apple cart. Especially step 3 may spell their spell their doom, along with Sony (stills, consumer) Imaging and their ludicrous lens prices.