It's been discussed throughout the comments here, go back and read them. Several people have explained how easy it is with a small and light camera, in addition to those of us who use our cameras for other things like video.
It's not categorically better though, it's just the way they're used to. When I use my 90D for photography I don't even touch the viewfinder, let alone put enough pressure on it to brace the camera. I imagine for some people that is necessary, but it's not universal. Perhaps with heavier camera gear it might help, but we're not discussing heavy camera gear here, we're discussing EF-M and whether a viewfinder has any inherent benefit over other options. As has been shown by the many posters not set in their ways, there is no inherent benefit, just tradition and training.
Also, being dogmatic would be to insist all cameras must have an EVF. I'm not saying all cameras should not have one, I'm saying there absolutely is a place for a compact camera without one. An M6ii would not be made better by adding an EVF, it would be made bigger, which is against the design criteria of that device.