Thom Hogan has written a great article about why he continues to shoot with Nikon DSLRs over mirrorless cameras in most situations. The same reasons could be written for shooting with a Canon system. While I had my “Sony phase” for a while, I was never happy with the results when compared to Canon DSLRs. This generally comes down to what I like to shoot, and as Thom says, that may not be the same things you like to shoot.
For the record, I do shoot with a Leica Q mirrorless camera, and I think it's the best small full frame camera out there for my uses.
From Thom Hogan:
Most of the mirrorless system issues I note above will tend to go away with time, as technology “solves” some of the problems, and digital cameras evolve even more than they have.
But DSLRs have been benefiting from technology moving forward, too, so it’s not as if mirrorless is trying to catch up to a stationary target. The D5/D500 proves that the target is still moving in big strides forward in some areas, and the DSLR/mirrorless problem has become like one of those algebra problems you had in grade school: “If train A leaves the station headed west at 75mph at 1pm and train B leaves the station headed west at 100mp at 3pm, when does train B pass train A?” Read the full article
I am like a lot of you though, I'm eager to find out what Canon has in mind for a mirrorless system, whenever they decide to get serious about it.