I had quite a few printers over the years, some home build ones as well.
But even with my near new P1S I run into prints that are less than acceptable at times.
From my experience bad looking VERTICAL walls can be caused by an endless list of issues, not all can be fixed.
The filament quality and how dry it is play a vital role.
But also the entire transport chain, like the tubes and extruder.
I had a Flashforge that started to produce all sorts of problems…
In the end I figured out it was the actual motor for the extruder dying…
With my P1S I struggled badly when I tried some old filament that was kept in a sealed bad with silica gel - it was TOO dry…
One of the biggest issues in the 3D printing world is still repetition…
We expect that all lines will follow the exact same path for a wall - but quite often this does not happen…
Let me try to explain:
If the filament extrudes without the required accuracy and consistency the wall can’t end up perfect.
Unless this actually IS accurate you can never tell for sure whether the defect is caused by how the filament comes out or by the actual nozzle position.
I had no issues getting ‘perfect’ prints from a threaded rod Prusa, slow but great…
The more speed, the higher the chances of things getting messy 
And like it or not: Calibrating a roll of filament PROPERLY can be hard, but that is nothing compared to properly calibrating your hardware…