Golly that is a sweeping statement but perhaps you're behind the times.
I suppose it depends on what DSLR and mirrorless camera you compare and by the way the mirrorless camera doesn't have to be a rangefinder style camera as SLR style cameras are available too but generally speaking as mirrorless cameras now run from MFT sensors and indeed smaller through APS-C and on to "FF" I think that the image quality is there and so are many other features and abilities.
Ergonomics and the OVF v EVF debate can be done to death and people will never agree but excluding image quality for a moment I thought that DSLR's only had a clear (or clearish) lead in focus tracking and battery life. Everything else, arguably, may be up for argument