There is a large overhead in SAS as it was designed for HDDs where the latency impact was not that critical. The next bottleneck for SSDs after the move to NVM

There is a large overhead in SAS as it was designed for HDDs where the latency impact was not that critical. The next bottleneck for SSDs after the move to NVMe is the limited number of channels from a controller. NAND is pretty fast but it is only getting slower, the key to make SSDs fast is parallelization between dies and a the bottleneck is the changes to get to the dies. Optane does get faster speeds by replacing the media with a faster one but for now it is not price competitive for most users.