SNR (i.e. DR at base ISO), resolution and strength of the colour filters are the three sensor-based factors that affect technical image quality at any given sensor size. Of these, SNR (plus the read noise contribution to noise) is probably the most important. Resolution matters for large prints and heavy cropping, and absolute colour accuracy matters for specialised things like art reproduction, but SNR matters for almost every application. Not just for high-DR situations, but also for image quality in standard DR situations at high ISO (you lose 1 stop of SNR for every step of ISO gain, although the biggest contribution to Canon's low-ISO DR weakness is read noise, rather than a difference in underlying SNR) and standard DR situations in anything other than white light (individual channels can get pushed or pulled by several stops just for white balance).
That said, the 6D2 was never going to be a ground-breaker, and not a good product by which to judge the state of Canon's technology. It's an entry-level full-frame camera, like the D610 and A7ii, designed to be price-competitive against the higher-tier offerings and for users who want to take nice photos in non-challenging lighting conditions, but who don't come close to pushing technical limits either in ISO, DR or AF. For instance, such a sensor or body would be perfect for a studio photographer with complete control over lighting, who has better things to spend money on than a body with unneeded DR, ISO or AF capability. Better to add a few more lights or accessories in that case, or a faster PP workflow.
The 6D2 sensor would have been designed with these users, and cost savings, in mind. Canon still has older fab plants which can make these sensors, but not the newer ones capable of making sensors with column-parallel, on-sensor ADC which have base DR in the same ballpark as sensors from other manufacturers. Better to use these fab plants to make sensors for a product which doesn't need a higher-grade sensor, while saving the higher-grade lines to make 5D4, 80D, 1Dx2 and future 5Dx2 sensors, than to leave them sitting idle while taking up higher-end capacity which could otherwise be making sensors for products which really need them.
I would expect the 5Ds2/other 5Ds replacement to be a much better gauge of the state of Canon's technology than an entry-level body which doesn't even pretend to be aimed at users who push technical boundaries. If it can hit 14 stops of DR (at 1:1 SNR, which is the level DxO uses in testing) while reaching 60MP resolution, it will be a competitive product, irrespective of what Sony brings out.
