SAS is basically two channel SATA with independent command queues, and can drive SATA drives, but SATA can't drive SAS.

SATA at 600MB/sec is plenty fast for contemporary mainstream server applications , which you can scale up with RAID 5/6/10 with some error resilience.

For higher throughput (plus more IOPS generally), SAS RAID comes into play. AI and processing servers generally come with NVMe disk stacks, configured with mdraid / RAID 0 generally, because the data is generally ephemeral, so losing the data is highly unlikely. You restart what you do on an other server, most of the time.

There's probably an FPGA or fast DSP which can handle signal/protocol translation with some state handling coprocessor on board, not unlike a (spinning) disk controller.