Mirrorless obviously is more compact. Add a 400mm lense and it's suddenly not so small. The larger DSLR body makes a good grip for larger lenses. DSLR still has advantages. However Sony does some superb mirrorless now that rival DSLR.
If I wanted lenses in the 12-80mm range for walkaround I'd take look at Sony mirrorless. The Canon EF-M lense lineup is not very vaste at the moment.