I don't disagree with your reasoning, because it's clear that Apple is including polaris-compatible drivers in Sierra.
But if we follow the logic to the end, it means that the MBPs are not delayed at all, since we all knew that macOS Sierra is coming out in September, and presumably so did Apple. So basically, it was the plan all along: wait for Polaris, make macOS compatible with it, then ship redesigned MBPs.
The only morons expecting anything else are the ones (like me) who spammed a poor macrumours thread for 740 god forsaken pages while waiting for the redesign. haha!
Truth. Right there!