Yeah whist I don't think anyone blames you for Sigma delays...its such a monumental task I can scarcely believe you're even attempting it. Such longstanding effort for a project is pretty crazy. Should be pretty obvious to anyone who looks at median now and then that Sigma is still a long way away since we are getting lots of large content releases recently which would be bundled into Sigma if it were close. Since the dev team is small obviously can't simultaneously pump out both content streams.
As for who to blame I nominate Rishab.