We don't know yet. There are no public technical details (that I know of) for H266 yet, but if I recall H265 gave the same 50% reduction in bandwidth claims, and for years people stuck with H264, because it was higher quality due to dropping off less subtle parts of the video you really want to see. Only in the last couple of years has H265 really started to become embraced and used by piracy groups. Frankly, I don't know what changed. I wouldn't be surprised if there was some sort of H265 feature addition that improved the codec.