In many instances that last stop can make a lot of difference.
However, in just as many instances we are increasing contrast in post and therefore removing a stop or so of DR. It's a valid thing to do when achieving certain looks.
I still don't think there is any DSLR/mirrorless camera shooting lower bit rates or codecs that can really compete with the USABILITY of the RAW on the BMD cameras.
If there was, I'd own one.
That being said, I am seriously looking at the GH5s as a "lowlight needs companion camera". Not an "A" camera. Mainly because I wouldn't have to change a single thing about my lens situation to add it.
But I need to get a hold of one and do some shoots first, because with my relatively fast lenses and the Speedboosters my BMD cameras do pretty darn well in low light already.
So the GH5s would have to be A LOT better for it to be worth it. But from the footage I have seen so far...it might be.