Erik,
Keep in mind that this is just one specific test, done in unknown conditions, using a specific camera model, unknown tripod, and long lens (how was it supported?). I would not extrapolate from this to a general conclusion about all SLR cameras and/or mirrorless cameras.
If you use a 5DsR with a 200mm around 1/45s, with the same tripod, it can be of value (as it is for the person who ran the test). The main benefit is to highlight a problem area with that particular lens/camera/shutter/tripod combination where additional care may be required. Additional testing would reveal possible solutions such as additional lens support, a different tripod, or maybe a different camera plate.
Mirrorless cameras are not immune to this type of problem. One of the reasons why you read so much about shake is that photographers noticed that their mirrorless cameras were prone to it at certain shutter speeds.
EFC is one technical solution to a specific issue, but it is not without compromise. Sony users report that the current implementation introduces colour artifacts with some non-native lenses, and that it reduces dynamic range (by raising the noise floor, I presume). It is not a pre-requisite for sharp images in most cases.
Getting back to the main point, the choice between SLR and mirrorless should be based on user preference.
Most current SLR cameras can be used in "mirrorless mode," they can do the same things that mirrorless cameras can. Mirrorless cameras can be smaller and less expensive, but that's not always the case once you attach lenses and accessories.
I use either type, depending on what I am photographing. I don't feel the need to pick a side.