Here are my thoughts from a non-professional enthusiast. I've been shooting with a 7D II for about 4 years now and coveted the 5D IV ever since it was released. I thought it was going to be my next body until I tried an EOS R in a store a few months ago which opened my eyes. I realized that it is a very different camera that while seemingly inferior on paper, actually suited me better than the 5D IV. So I ended up buying an EOS R last month instead of a 5D IV. Take the following perspective with the appropriate grain of salt: I'm a long time 7D II user, new to full frame, and have never owned a 5D IV, although I have used one before. I primarily shoot landscapes, some macro, and some wildlife. A lot of my photography happens many miles from the nearest road, so I spend a lot of time carrying my camera and associated gear on my back.
Pros list for 5D IV:
7 fps (EOS R can do 8 fps without AF Servo, which is great, but 5 fps with AF Servo is less than I'd have liked)
Better AF Servo performance for fast, erratic moving subjects
Better weather sealing
Slightly better noise performance (But this is extremely subtle, far less than the difference between the 5D IV and the 1DX II, for example. A complete non-issue for me.)
Dual card slots (would be nice to have, but not an issue for me)
Traditional Canon aperture adjustment wheel around set button (I much prefer this location to the EOS R's top mounted dial)
Better battery life (Although I get well over 600 shots on a battery with my EOS R, so this isn't an issue for me. If you were shooting in continuous it would be even more.)
Pros list for EOS R:
Access to new (and excellent) RF lenses (and EF lenses with an adapter)
Smaller and lighter lenses on the horizon (see the announced RF 70-200mm f/2.8 IS)
Real time exposure preview through the EVF
Excellent focus accuracy (no AF adjustments for each lens to compensate for the separate phase detect system in DSLRs)
Excellent low light AF
AF points cover nearly the entire frame
Autofocus at apertures smaller than f/8
Eye tracking autofocus
Touch screen AF point control (I was surprised to find this faster than the joystick I'm used to, but will be very annoying when shooting deep into winter)
Smaller and lighter (big deal for me)
More comfortable grip (especially with the L-bracket I chose)
Tilty-flippy screen
In body battery charging (although I don't expect to use it)
Able to shoot video through the EVF
Faster write speeds to cards (see cameramemoryspeed.com)
I look at this set of differentiating features and see that the EOS R is a better camera for me. You may feel differently, but that's your prerogative. You are not being forced to buy it. Some of you might want to wait for the upcoming pro level mirrorless Canon, but some may find that this camera will do what they need. (I love the idea of a higher resolution full frame body, built more robustly with better weather sealing, and with in-body-image-stabilization, but I knew that it would be well beyond my budget, so I have no regrets jumping in with the EOS R.)





