Solid-state lasers produce a rectangular spot, not the nice circular one you’re thinking of, so the narrowest cut will be different in the X and Y directions.
Stripping paint off copper will require testing to find the ideal combination of speed & power. A few Material Test patterns should help you get better results:
Also: make sure the machine has using good ventilation!
That is excessive, because the spot size will be on the order of 0.1 mm, which is 10 pixel/mm or 254 DPI. Using higher resolutions won’t produce much benefit.
The first picture looks like you haven’t yet measured and enabled the Scanning Offset correction:
But you’re off to a good start!