The whole internet seems to be comparing the A7SIII to the R5. Makes no sense, but I think Canon marketing is at least in part to blame for that.
If I look at the website of Canon Japan, the R5 features pitched there from top to bottom are roughly (some are described in more detail than others):
- sensor and processor
- ISO range
- Dual Pixel RAW
- HDR PQ HEIF
- IBIS and EF compatibility
- 8K and 4K video
- AF including animal AF
- Framerate
- Battery
- Ergonomics
- Durability
- Connectivity/wireless
Video is one item out of many and it comes at 6th place. This is the description of a stills camera with video functionality. I would agree with the message being conveyed there, this is how a 5D-line successor should look like (although in my opinion wireless capabilities should have a more prominent role in 2020)
However, the hype-building marketing before the R5 launch focused mostly on 8K video, a strong contrast to the above. The internet then just amplified the hype.
The R6? It's a mini-1DXIII for less than half the price with excellent 4K (limited in recording time though), launched at the same time as the R5, and it has never been mentioned.
That's could be fine, but then you have to deliver. And I am not talking about performance. Some of the A7SIII video "reviews" seem to be well prepared, indicating that the cameras were available weeks before launch and could be tested thoroughly.
R5 and R6? With the exception of Canon ambassadors, the others got mostly pre-production models for a limited time and were not allowed to test everything. And likely they got them after the A7SIII. That will inevitably lead to the type of comparisons we are seeing now.
Youtube is not everything and such thing can happen, but add this to a somewhat incoherent marketing message and it is no wonder that suddenly 12 MP on the Sony are more than enough for stills, while 20 MP on the R6 were a disaster. Go figure.
As usual, dust will settle at some point once people start using the tools for the purpose they were designed for.