Help with understanding codecs and sensor sizes.

4K has 4 times the data of 2K (8MP per frame vs. 2MP per frame) so zooming in on the frame (cropping) in the editor will be better for 4K than 2k. Sensor size has more to do with the dynamic color range of the image, more gradations of color with a larger sensor and also better low light capability at lower iso’s and therefore less noise in the image. Personally low light can be solved with lighting to shoot at base iso with any sensor. And dynamic color range can be addressed with color grading, so for me, 4K trumps sensor size.