The dynamic range of these cameras is pretty much identical, the C500-2 may have 1/4 of a stop mre shadow response but it's too small to call.
Both cameras are good from +3.5 to -2 stops, I measured this by looking at where the small square inside the white square on the stress test chart vanished. This established the highlight limits. The shadow end was more subjective but was based on where the blacks started to move up and how noisy the waveform looked.
I set the zero frame by looking for the frame that was nearest to 25 across in Resolve using ACEScct and a rec709 ODT. In the case of the C500-2 this was at the zero exposure point, with the FX9 this was at the plus 0.5 of a stop point. All references plus and minus are based on this zero figure.