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What lead are you talking about? Canon's sensors were a running joke in the past 5 years comparing to Nikon (that used modified Sony sensors), manufactured in 3 generation-older process than their competition. Seeing e.g. D750 vs 5D MkIII in low-light was an eye opener. The only selling point of Canon remained their unique "pleasant" color mapping (and photographers getting stuck with older Canon-only lenses/strobes…
Canon's sensors are decent, not a running joke as you say. But yeah they are known more for their colors (which is actually very important). Sony has destroyed the competition with their sensors though, and has really pushed the boundaries, at least until recently with that 50 mpix sensor that Canon released. Haven't researched that much though, I'm a few years behind myself. That said, Canon has historically been th…
I, too, surprised myself by recently purchasing a 6D (I, not II -- why increase weight and dark noise?) on both lens-selection/lock-in and quickness concerns. I was surprised to find that I loved being able to leave the camera switched on all day in the mountains and draw/shoot/stow in seconds, with 1000+ images on one battery. Barring substantial advancements in sensor/display power consumption, no mirrorless camera can match that property. Furthermore, it is an instrument I can handle/adjust quickly and reliably with gloves on in harsh conditions. For a week at temperatures between -20 and -30 C, the 6D (and iPhones kept warm) operated normally while friends with mirrorless cameras suffered shutdowns.
The three things, from my perspective, that Canon really lacks are 0.5-1 stops of dynamic range in the sensor (SNRs are competitive across all brands, an underappreciated fact), silent electronic shutter, and Sony's incredible array of on-plane focus sensors and focus algorithms (Canon's DPAF may actually compete, if turned loose/optimized further). Sony's eye-detection AF must be a game-changer for portrait photographers.