I really see their tactics play out differently. Unless your going webway portal my rubric deployment will be straightforward where as SOTs can DS. Also utilizing them in cc where appropriate against specific units sets them apart.
I dont have a diverse meta and play Eldar quite a bit so my sample size research is not great though a unit of SOTs provides a great bully to apsects and other Eldar units with a warptiming Termie Sorcerer. They are situational and there is a need for them to be flexible like a cataphract, though with with DS, WT, even DMC can offer that.
I also play against DA and GK so a MVB to have str5 vs T4 buff I am hoping can do similar work.
That is fair, I often forget their melee ability and with some support they become relatively formidable. I do love fielding them I just hesitate in many of my list builds.