I would agree with you, but it's hard to take that look on Palpatine's face when he talks of Plagueis's murder as anything other than fond reminiscence. The subtext was clear to me even as an adolescent watching it in the theater. But the fact that he presents it to Anakin as a legend does give him cover when he admits to Anakin that he himself doesn't know the secret to cheat death. Anakin himself doesn't necessarily realize that Plagueis was probably Palpatine's master. That's something a lot of critics miss.