Is drawing lines/paths just something the GPU is bad at and that one
should not try to hardware accelerate, or am I likely doing something
wrong that causes the bad performance?
Paths are always rendered using the CPU. When the app is hardware accelerated this means the renderer will first draw your path using the CPU into a bitmap, then upload that bitmap as a texture to the GPU and finally draw the texture on screen.
Lines are entirely hardware accelerated. Instead of using a Path I recommend you use Canvas.drawLines() in this case.
Is there anything I can do to draw such huge paths with acceptable
performance?
You should either use Canvas.drawLines() or render the path yourself into a Bitmap that you manage.