I often feel like I'm the only one who thinks the 5DIV is lightyears ahead of the 5DIII. The 5DIII was incredible. I had two and loved them. It was so nice to have two and switch cameras at events and not (often) switch lenses. But now, with having one 5DIV and one 5DIII, I never use the 5DIII - it's just backup. The 5DIV images are so far ahead of the 5DIII it's silly.
I'm going to stop here and mention that when I got the 5DIV, I noticed the bump in resolution immediately, but it took me a long time (3 months daily professional use) to understand just how much better the sensor was in the 5DIV. Why? Because the files looked and worked the same between the two cameras. It was hard to tell the difference, because the transition was so easy. That's what makes Canon so amazing. I picked up the 5DIV and it felt and worked exactly like my 5DIII. Exactly. Within 48 hours, I was using the new camera as my primary camera for paid work.
But, I think this is also why Canon gets lacklustre reviews... There is no eye-poping differences that are immediately apparent. The cameras all feel the same. I assist a photographer who uses the 1DXII and I can pickup his camera and shoot with it without hesitation. It feels and works the same. This is a huge positive for working professionals. But, in the age of viral internet reviews. Consistency, reliability, and smart thinking just aren't 'sexy'.
Let me reiterate that in a different way. Canon changed their sensor design and yet they kept the same colour science. They increased their dynamic range and file workability and yet, those who work with Canon RAW files can keep their workflow. To me, that's a fantastic implementation of a new feature.
Back to my 5DIV... when I used my 5DIII alongside my 5DIV, as I process the images, I now immediately know which files were shot on which body. The 5DIV has blacks and an amazing range of details in the highlights. Not to mention, once the files are being worked on, there is a massive difference in the processing latitude of the files. The 5DIV files feel like rubber bands.
I am curious about other brands, don't get me wrong. Sony's eye-AF, looks incredible. But, I can't get over the rest. Everyone I know who upgrades to a 42-50mp camera (A7Rii, A7Riii, D850, 5DS) ends up needing to upgrade their computer to maintain processing efficiency. That's a massive expense for most working photographers. Not to be scoffed at, if you aren't already needing an upgrade. And yet, going from the 5DIII to the 5DIV, I've not felt any significant speed/efficiency decline in my workflow. And 30mp is a lot for what I deliver to clients. A lot. More than 98% of my jobs require.
Not to mention, everyone I know who uses Sony A7*'s professionally has had corrupted cards. Everyone, and not just once. That would give me a heart attack during a paid shoot. I could not handle the stress. Yeah, most of the time, the files can be recovered, but not all of the time. That's not a little bug.
I could keep going... but I won't. I'm just surprised that Canon, who makes cameras that work (no corners cut) gets slagged on so often. The other's make great and exciting cameras that have a small (yet tangible) list of sub-standard issues. But, those issues seems to be overlooked, or at least shrugged off, because of a few 'innovative' marketing tool features taht Canon doesn't have, because 'they don't innovate'.
And, as a side topic, perhaps someone can explain to me why the 6DII feature list was such a shock? The 6D cut into 5DIII sales. No doubt. I know enough people (myself included) who compared those cameras against each other when the time came to purchase a body, to understand that the difference was not enough to segregate their market placement. So, why did it come as a surprise that the 6DII held it's intended market position (to be the 'entry level' FF camera)? If you want more bells and whistles, you buy the 5DIV. Seems straight forward to me. Seems like good business practices for Canon, no?
/Rant over...