I think you may be conflating the Octovalve with the introduction of a heat pump in the Model Y. The latter is what will contribute to the greater efficiency in that purely resistive heating (which is power hungry) will no longer be the sole means of providing cabin heat.
The Octovalve is simply a packaging/cost-reduction optimization. While it is indeed part of that overall thermal management system, it doesn't really contribute to efficiency, but more so space/weight/part-count savings.
People made the same mistake with the introduction of the "Superbottle" on the Model 3... while clever in that it combined a number of previously separate components in to a single unit, it didn't actually introduce any new capability or efficiency... again it was design optimization...