Let me address the parts of the puzzle. lets look a the image chain from front to back. If you have a high resolution lens more information will get to the sensor, if you have a lower resolution lens it will lower the amount of information (data) that then sensor sees. Same goes for focus. Being in focus increases contrast, higher contrast is more information and that makes for more data. Being lower res reduces the processor overhead. If we were to record each and every bit that comes off the sensor and we are shooting 4K (4096x2160) at 24fps, there are three color channels (YUV) and each one is 8bit's deep (10bit would be better and 14bit is what is used for feature and TV production) and that gives a frame file size of 26.5MB. One second is 637MB or about 300Gigabytes/hour.... That's a lot of data that the processor has to wade through. If the image has a bit lower resolution you will limit the about of data since your GOP I frames have less difference across the frame. Now you have to compress that and that's getting rid of a ton of data and that's where codec's come into play. Some are good most are bad but in the end your grouping similar tones in the image and writing a key frame that describes the entire frame then your using those groups to only update the areas that have a change (GOP compression) I could get into I Frames P frames and B frames but it all has to do with motion and there where the variable bitrate comes in that is confusing Tuna.
Lets look at why Bitrate is an important number it gives and indication of compression ratio. Yuneec says that their cameras output 50Mbps or about 102/1 compression ratio. When they first advertised the capabilities of the CGO3+ they said it was 100Mbps which would have been 51/1 compression ratio. The Yuneec Raw is only giving you about 29Mbps which is 176/1 compression ratio. Compare those numbers to the P4 and the GPH4B which are running 85/1 compression and you start to see a performance metric.
In the end it's about color accuracy, contrast, and focus which is collectively called image quality and all of those are affected by Bitrate. Saying that Bitrate isn't a performance indication is a sign of not understanding the chain. One other thing to consider, if Bitrate wasn't important Yuneec wouldn't have advertised 100Mbps then changed over all their material to show 50Mbps...