You forgot a few points! I have 13 that I found to be notable, and I know I am missing a few others. Any one item may not be a huge thing, but when you take all of these together as a bundled deal, it is a pretty large step forward. I use most of these on just about every shoot.
- The 5D4 AF system is more surefooted and faster than the 5D3
- It can lock in lower light AF better
- f/8 AF on many, many more AF points
- High ISO is better as well, as is dealing with shadows at low ISOs
- 8Mpx more resolution for added benefits
- WiFi control and file transfers has actually been great
- The touchscreen is a godsend
- Better metering system
- USB 3.0 port for faster transfers
- New AWB setting that works very well over the old AWB setting
- The SD slot isn't handicapped speed-wise as the 5D3 was
- Flicker control and DPAF are the proverbial icing on the cake
- Cropped 4K video
- Fully working auto ISO in M mode with EC
- 1 extra FPS, whoopity do, but it is an improvement
The 5D3 is a great camera (I had one for a couple of years and shot NBA ball with one), but it won't do what the 5D4 can do, the 5D4 is just better all around. I wasn't sure about spending $2900 for the 5D4, but bit the bullet last year, and never regretted it since.
RE: File sizes: Greater resolutions means more versatility in a) detail rendering, b) noise handling, c) more cropping power, and d) more versatility in what can be cropped out, ie more choices depending on the content. Besides 22Mpx vs 30Mpx just doesn't tax the system all that much more. The CPU will run a bit harder and longer and the fans might kick in periodically, but that 8Mpx isn't going to cripple your system unless it is more than 5 years old.