I returned my first copy of sigma, got the 35L, returned it, and then went back to sigma.
I have to agree with a lot of what you said in the review. The canon's construction does feel more robust. I definitely felt more comfortable with it than the sigma. However I personally found the level of CA of the Canon to be excessive below f2.8.
Most reviews have concluded that the sigma 35 is the winner when it comes to sharpness and value. What no one can prove yet is reliability and longevity.
Until 35L II is released and its price lowered significantly, sigma would my choice for now.
5DMK3, M5, 24-70 2.8L II, 16-35 F4L IS, 70-200 2.8L IS II, 35F2 IS, 135L, 70-200L F4 IS, 600EX-RT x2, 430EX RT, EOS M IR converted, efm 11-22, efm 28 macro, efm 18-150, Fuji X-T20, Fuji 35 F2, Fuji 10-24 F4