Yeah I don’t expect it to be 100% with the drivers being so weird. I’m almost sure it isn’t a hardware problem, just the drivers. What might help even more is if you could map out the response in finer detail. That is, maybe your pen driver isn’t even giving you back a linear response. So you’d have to create a curve in the global pressure mapping to correct for that if it was the case. You might even just start with a curve and see if that helps. Try a convex and a concave and see if either of those help.
Brush editing can be pretty complicated. The best thing is to look at brushes that you like and figure out how they work; look for which settings and inputs are in effect. You might want to open the brush file (.myb) to easily see which settings are being used.
Then play with the settings with the instant preview turned on. I don’t think photoshop brushes will be compatible any time soon. Mypaint doesn’t even use custom stamps, every brush is based on little circles or ovals, basically. I agree we need a lot more tutorials though. I have a few on my youtube if you dig around. Here’s a flatbrush tutorial that also is a good overview of general brush editing. You’ll need an alpha build or compile from current git source for some of these settings, though.
