Update of progress
So as I'm waiting for the etune to be completed I couldn't help but continue to mess around with ATR.
I've managed to get rid of the overboost, especially the large one around 4,000 RPM's. And throttle closures, even small ones, are next to gone.
However as we can see the oscillations remains. It seems like as soon as boost mean hits requested boost, the DME overacts and knocks boost back down drastically as soon as the numbers match. Maybe an overreaction of the PID system. I'm not really sure as I'm just learning but wanted to share my findings so others can possibly benefit.
Before and after data plots attached as well as the most recent WGDC Base in ATR.