SS's effect on autoattacks isn't significant enough to make it the best stat. Or even especially good. It's not terrible like it is for some jobs (MCH and RDM, for example) but it's not great.
BiS sets taken from The Balance:
http://ffxiv.ariyala.com/18M7M - 2.06 - Eureka
http://ffxiv.ariyala.com/17BD8 - 2.06 - No Eureka
http://ffxiv.ariyala.com/18M7P - 2.05 - Eureka
http://ffxiv.ariyala.com/18M7Q - 2.04 - Eureka
http://ffxiv.ariyala.com/18M7S - 1.99 - Eureka
So there's a bit of flexibility there, and SS is generally valued somewhere around what Determination is -- that is, worse than Direct Hit and significantly worse than Crit.