The structure of most endmills, makes them less effective in their middle when moving like a drill.
This issue would be eluded a bit if the Z moves into the material were not straight down, but rather a Ramp.
A very simple Solution to this would be to take each Z move and do it along a part (like 10mm) of the next XY movements, and mill the XY path to full dephth in a second pass after ramping.
Simple XZ-Plane Example

The structure of most endmills, makes them less effective in their middle when moving like a drill.
This issue would be eluded a bit if the Z moves into the material were not straight down, but rather a Ramp.
A very simple Solution to this would be to take each Z move and do it along a part (like 10mm) of the next XY movements, and mill the XY path to full dephth in a second pass after ramping.
Simple XZ-Plane Example