I had this Pie update yesterday 2018-10-12. At first I didn't pay attention to battery issues, but instead I was very unpleased with Pie UI, namely QuickStep, which I then changed to and tweaked with Nova. Then, I started to notice the severe battery drain, which I in my mind at first blamed to Nova. But, instead, as I just noticed, it's the Pie itself.
With Screen brightness as low as 40% and all battery savings to the max, I only get about 10 hours of forecasted charge with no usage, as opposed to Oreo's previous settings like 85-95% brightness and 40+ hours of charge even with more than moderate usage.
So something's definitely wrong here.
No, I haven't seen such flickering yet.