Video isn’t my thing, so I’ll leave others to comment on that...
The R is currently available new for £1220 body only, which is “super cheap” - a great bargain for any stills photographer. I use a R5 as my main camera, and a 5DMkiv as backup, but as I’m slowly switching over to RF mount lenses, I’ll probably sell the 5DMkiv and replace it with an R. It makes an excellent and very affordable backup to the R5, has a near identical control layout, and the specs and performance are more than good enough for 90% of the wildlife, nature, travel and landscape work that I do.
I agree that the Sony a7iv makes a great addition to their line-up. Obviously as a new late 2021 model, it’s going to have a superior specification and marginally better image quality than Canon’s 3 year old first attempt at an FF MILC, but the Sony is twice the price.
Sony make excellent cameras and gave Nikon and Canon the much-needed kick up the backside that they needed. But given the choice between the a7iv and the similarly priced R6, I’d definitely go for the Canon. Similarly, given the choice between the R5 and the £6000 Sony a1, the canon for me is the better choice. Sony cameras are very full featured and perform very well, but IMO they are very overpriced.
It’s great that we have so much choice these days, there literally is something for everyone, no matter what their requirements, and with FF MILCs starting at £950 and going up to £6000+, there is something for everyone’s budget too.
As for brand, it’s very much a personal choice, as you often find 2 cameras with near-identical specifications that have entirely different handling characteristics. I’m happy with my choices, and I hope Sony and Nikon (etc) users are equally happy with theirs.