While I agree with you that the A73 is a good 'all rounder' this statement about 4k is false. People do use the 5D4 and R for 4k video. In fact, some of those people would say the A73 is unusable for them because of the low bitrate which limits their grading options. Under heavy grading A73 footage starts to fall apart where footage from high bitrate cameras like the R, 5D IV, and XT3 remains solid. The crop and lack of high speed 1080p are certainly annoying but the R can produce good 4k with good lenses. (The crop means you're stressing lenses more. I think that's why there are some really poor 4k R examples out there. Potato Jet basically said as much, that the R can produce great 4k if you're using great glass, and he had the video samples to back that statement up.)
Never the less, the A73 is a very well spec'd hybrid camera. And I hope Canon takes some of the tech in the 90D/M6.2 and uses it to make the R mark II a FF 4k beast.
Hm I realy cant agree on the 5D IV (and R, which is 95% the same).
While we did use it for 4k video productions (alongside my 1DX II) it was REALY a pain in the ass. The crop is not even the biggest issue (while it certainly is a big pill to swallow). You can work around it with APS-C lenses like the Sigma but the options are somehow limited, at least if you mainly use Full-frame and dont want to restock.
Its the ludicrous Rolling shutter. Its REALY not okay. There is just no way around it. The unhandy codec in the 5D IV is another point (though this was fixed in the EOS R).
The higher bitrate is in reality not that much of an advantage. While the image of the 5D IV (and especialy 1DX II which truely shines at 4k60) is a bit more robust as the Sony in grading, its not that day and night difference. The Higher bitrate is only there, because of the VERY inefficient MJPEG codec.
One big plus on the Canon is the much better color rendering. The "green skintones" are not a myth and the canon realy performs much better than all Sony A7 cameras.
One INCREDIBLE failure is btw the 1080p mode in the 1DX II and 5D IV. We did some comparisons and its insanely bad :-D
However, in video mode the 5D is MILES away from the Sony a7 III which offers a way better balanced setup for a cheaper price.
The 1DX II is certainly better and the Cinema Line is obviously far better. But at THAT pricepoint there is simply NO all-in-one solution in the camp canon. Which put me somehow in a tight spot, where I didnt realy want to upgrade to a C200 (which is easily 9000-10.000€ with necessary accessories) but also didnt want to leave canon.....