OK, I see those tests. It looks like the C200 comes out at 16.1ms (tested) and the BMPCC6K at 6K comes out at 19.7 (officially). So, there's a difference there.
I'm not sure RS is a total dealbreaker with strobe lights. To be sure, it screws with how they render on video. But I'm not sure any wedding clients would be pissed off about it or consciously recognize that there's something wrong.
That being said - even if you don't notice a rolling shutter artifact, I still feel like a slower rolling shutter impacts your motion cadence negatively.
And I feel like the ratio of the rolling shutter to the frame rate is important. I feel like a lot of cameras have a sort of smeary looking motion in slow motion even if they look fine at normal speed.
Yeah clients probably don't care, more of a personal thing. In 5.7k the RS is lessened on the p6K tho so it may be on par with the C200, but I've never used them side by side. I've never understood or noticed motion cadence.