What's the point of 4:4:4 from a non-oversampling Bayer sensor? You don't have so much color resolution there anyway.
Your assumption is wrong. The chroma subsampling is not impacted by resolution. If you shoot 4:4:4, the sensor does not encode a chroma subsample into the file, so in that way you have the highest chroma space for post production. That's what cameras such as Alexas do in ProRes, regarding of the resolution of the sensor.
The C700 can shoot 4:4:4 if you shoot externally, which is the hassle people have about a $35k camera. It's in no way a bad camera - but you need to have a Codex recorder with its media cards, which put around $20k on top of the camera. You start to get inside Alexa Mini territory (at least used). If you go to 2K, you have a helluva camera that can shoot 2K 4:4:4:4 12bit in ProRes, which is awesome - but again, you kind can do that with the C300 Mk II by shooting 2K 4:4:4 12bit XF-AVC.
The newer Cinema EOS cameras (C300 Mark III and C500 Mark II) can shoot 4:2:2 10 bit (which is the intermediate codec) or Cinema RAW Light. There's no chroma subsampling in RAW format and that's one of the reasons why these cameras were received extremely well by the market: it's cheaper and it offers a more robust chroma subsampling format depending on your needs.
So, in other words, if you get an Alexa Mini and shoot 4K with ProRes 4:4:4:4 from its 3.2K sensor and a C700 and shoot 4K ProRes 4:2:2, the Alexa will get a better color rendition due to the camera not subsampling its chroma information, even though the camera is shooting from a smaller resolution imaging sensor.
On that same note, if you shoot 4K 4:2:2 from the C700 and compare to the Cinema RAW Light from the C200 converted into ProRes 4:4:4:4, the C200 will have more color information due to the CRL format not having any chroma subsampling at all from the get go, even though both cameras share the same sensor.
It's another story if you need to go through the trouble of shooting RAW and then encode into ProRes to have more color information than shooting directly in 4:2:2 10bit (which is more than enough for most web content deliveries).
Last but not least: The C700 sensor actually oversamples from 4.5K to 4K. It does not make a big difference but it does show a difference when comparing the internal 4K footage from the C700 and the C300 Mk II, per example, with the C300 Mk II looking soft (especially if you are trying to reframe it into a HD delivery).