This is akin to the old V8 engine issues.
Mirrorless has some extremely high advantages over SLR's in general mostly and I think its deliberately so, the fact that you can mount almost any modern lens to one and have it work.
. . .
As for the press corps issue, try nature photography, sporting events, WEDDINGS!!!
I see nothing but advantages witht eh only real disadvantage of the viewfinder issue.
". . . you can mount almost any modern lens to one and have it work"
One glaring exception, for me, you CANNOT use a current Nikon lens on a micro 4/3 camera (Olympus and Panasonic).
Last I looked, there were NO adapter that allowed communication between the lens and camera.
That means the lens is auto NOTHING; no auto focus, no ability to control the aperture from the camera, no VR, no auto opening aperture, and with the AF-P lens no ability to manually focus the lens (because the AF-P is focus-by-wire).
It is easier for me to use a 1970s manual lens on the Olympus, than a modern lens.
So while some combos work, other combos do NOT work.
There is another major issue, a comparatively short battery life, compared to a dSLR.
Depending on the camera/lens combo, it can be painfully short. 2-1/2 hours for one of my combinations, and even shorter for other camera/lens combos (from reviews). Yes, I can carry and do carry spare batteries, but for that one camera lens combo, I have to carry FIVE batteries, for a full day of shooting. And I have to pre-plan when to change batteries, so I don't go 'empty' in the middle of a shoot, which has happened. grrrrr

The basic problem is a mirrorless uses MORE power than a dSLR, but in order to keep the camera small, they did not use a LARGER battery.
Having said this.
#1, I just don't use other lens on my Olympus, problem solved.
#2, With technology advances, the power consumption might drop. But they could also put more power sucking stuff into the camera, off-setting the gain.
And the camera mfgs may finally bite the bullet and put larger batteries into the cameras.