Two very comparable cameras with the same sized sensor: http://camerasize.com/compare/#724,718

Sony's mirrorless camera is also more compact than SLR cameras with smaller (APS-C) sensors: http://camerasize.com/compare/#724,708

They're also quieter (no mirror slap) and having an electronic viewfinder allows you to see what will be recorded. For example, you can directly see the effect of a longer exposure or higher sensitivity.

Their batteries last significantly less and the lenses tend to be bulkier than equivalent DSLR lenses. This takes away most of the advantages.

Many people don't like electronic viewfinders either. They've gotten better, but it's not quite the same, at least not yet.

Video is superior on mirrorless though.

That's not because of the cameras being mirrorless; it's because (for Canon anyway) they purposely gimp video on their DSLRs to get you to buy their Cine-EOS cameras.

Which is why all the kids these days are using Magic Lantern and unlocking the actual potential of DSLRs by shooting uncompressed 14-bit "raw" video.

Not working though is it? Mirrorless are making huge strides in video

Strides which do not result from them being mirrorless. You should understand that the mirror does not get involved at all when doing video with a DSLR. So, all of these 'strides' can and have been replicated in the next version of the cameras.

I'm not sure what your point is - it's mirrorless that have really pushed the tech on here at least at the cheaper end of the market. It's my understanding that Lumix G range for example has been widely adopted for video in a way that SLR has not. Are you saying these users will defect to SLR with a new generation? Can't really see why, since all that going SLR would do is introduce some extra mechanics they don't need.

DSLR/Mirrorless is unrelated to sensor size. Sony makes 35mm mirrorless cameras with great sensors, just like more or less everyone making DSLRs also makes some with sensors smaller than 35mm size.

And lets not forget the Hasselblad and Fuji medium format (cropped "645" at 50MP for the current models) mirrorless cameras either.

It gets rid of the flipping mirror.

As in most hardware devices, less moving mechanical parts is an advantage. Sensor size is unrelated these days.