Can you explain what limitations that you see?
I think these cameras especially the R6 can compete with the Sony A7S3. In particular, we still have to see if Sony is able to put 4K60 in the A7S3. If they do, they may neet fans or the camera may also overheat.
On a film set there are a lot of things that a non-dedicated video camera lack that people require, set depending.
Timecode sync, I/O for SDI XLR, etc. What I'm trying to get at is that proper film sets aren't going to roll up with a Canon R5 and no other cameras and use it as an A cam. Key here is proper film sets.
As for the R5 vs the A7SIII, they aren't even trying to compete in the same class. The R5 is a killer hybrid stills and video camera where the A7SIII is a video camera that has stills capability. With all the people complaining about the R6 only having 20MP, why are people even throwing the A7SIII into R5 conversation? You know? These are different tools with different focuses.
The A7SIII is going to be a wonderful and incredible camera and a lot of people are going to buy it.
I work primarily in video, for most of the work I do Autofocus isn't important so frankly I still absolutely love using my GH5 and even my GH4. These handle long conversations and things amazing and I still have the 150Mbps 10 bit codec if I need to run for like 2 hours at a time.
I sold my EOS R, which I got to be a stills camera with decent video functions when I needed it, to get the R5 because it's going to do exactly what I need it to. It's going to be a stellar professional stills camera with some really useful video functions I will use often and enjoy having at my disposal.
I have some solid EF glass that I still love, such as the 70-200mm f2.8L IS II and use it regularly on my GH4 and GH5 and while I started photo and video back in the day on the 7DMKI, which I still have, I have always enjoyed Canon cameras for stills and often have rented them or used them for work. So the R5 is a no brainer for a camera that should last me many years, be capable of decent video projects, and handle 90% of my stills work I need.
If I'm shooting for someone on a set, we often will rent a C200, Ursa Mini 4.6K, or similar. I also really enjoy the EVA-1 and S1H for dedicated video cameras.
I just don't know who these people are and what they actually do when they keep focusing on just this 8K and 4K/120 spec... It's already so annoying to read.
This was long-winded, I apologize. haha