Hello and thank you for the reply and advice!
After splitting the object into smaller parts and trying further PLA manufacturers (Polymaker, Fiberlogy, Extrudr, Filamentum) I’ve concluded that this has nothing to do with filament quality. I’ve printed over 10 benchies and test cubes per filament brand with different settings to fine-tune every possible error.
So the next thing on the list was squaring the axis and trying to rotate the model, this has not helped. I am not sure though how tight the belts must be, I’m currently looking into printable models that attach to the belt/rods and indicate belt tension.
Here is what DID help and what I would advise doing if anyone gets similar inconsistencies:
If your printer is clean and you’ve gone through the list above, do:
- set outer wall speed to 40-60mm/s (inner walls can stay at 150-200 without any problem)
- set outer wall accel. to 3000mm/s^2
- turn off ensure vertical wall thickness
- turn on precise walls
- outer/inner/infill order
Even though the flow values are basically coefficients when calculating flow, with these lower outer wall speed settings I set the Bambu PLA profiles flow to 0.93-0.94 (depending on Basic/Matte). This should be a confusing idea, however, this makes sense (see CNC Kitchens video: BambuLabs 3D Drucker sind ZU SCHNELL! Festigkeits- & Oberflächenprobleme lösen - YouTube). With the same reasoning, I reduced the temperature to 210°C.
With these settings I experienced increased stringings when printing multiple objects layer by layer, this however is not a problem as strings don’t go through inner walls with these wall order settings. In worse cases, this was curable with retraction settings and different Z hop movements and wipe settings.
Achieved wonderful results with Bambu PLA Matte Black with non-visible layers at 0.2 layer height. (No matter from where the light hits the model, it looks like injection molding haha 
).
I will mark this as solved when I’ve made sure the printer is actually squared and this wasn’t the issue all along, so thank you for the advice!