A bit of research to share.
The Wacom driver applies a bezier curve to the pressure response of the stylus, called ‘Tip Pressure Feel’. In Linux Mint, there is no GUI to see this curve. Resulting, for me, in supplying GIMP with a non linear pressure curve. Which is not ideal, so I looked into fixing that. The setting can also be accessed via command line.
xsetwacom --get "device name" PressureCurve
PressureCurve x1 y1 x2 y2
A Bezier curve of third order, composed of two anchor points (0,0 and 100,100)
and two user modifiable control points that define the curve’s shape.
Raise the curve (x1<y1 x2<y2) to “soften” the feel and lower the curve
(x1>y1 x2>y2) for a “firmer” feel. Sigmoid shaped curves are permitted
(x1>y1 x2<y2 or x1y2).
Default: 0 0 100 100, a linear curve; range of 0 to 100 for all four values.
min soft setting ( marking 0 ) on the slider GUI
xsetwacom --get "Wacom Intuos Pro L Pen stylus" PressureCurve
0 75 25 100
max firm setting ( marking 6 ) on the slider GUI
xsetwacom --get "Wacom Intuos Pro L Pen stylus" PressureCurve
50 0 100 50
However there is a sweet spot at ( between 3 and 4, 3.5 ) that gives a linear curve
$ xsetwacom --get "Wacom Intuos Pro L Pen stylus" PressureCurve
0 0 100 100
Now you’re working with a linear curve in GIMP. You can set the pressure curve temporarily via command, but the driver quickly takes control and sets it back to the GUI setting. Anyhow, then you can do an adjustment curve in GIMP for fine control over the pressure response.