Wiggly Lines when using Pencil on iPad Pro

I recently purchased an iPad Pro primarily to use it as a drawing device because I needed to replace my Intuos 3 simply due to the fact that there isn't a working driver for the most recent MacOS. I figured an iPad Pro would be a better option over a Cintiq because then I'd also have the option to use it on the go in addition to using it with my Mac Mini via Astropad.

But I've run into a major snag: Horrible unacceptable wobbly lines. The attached screenshot is from Photoshop via Astropad (using a USB connection) and all of the lines were drawn using a ruler to negate any shakiness of my own hand. The vertical and horizontal lines look fine, but the instant I try to draw on an angle it becomes this wavy mess.

It should be noted that this same behavior has also occurs if I use the desktop version of Clip Studio via Astropad and when I use the iOS version of Medibang, so I have ruled out it being an issue with the software I'm using since they all do it. And the pen stabilization options in Clip Studio and Medibang help a little, but don't seem to completely fix the wobble.

Is this expected behavior (in which case, why did I pay $1000 for this device that claims to be made for artists), or did I just get a defective iPad or Pencil?

Additional note: I do not have a screen protector. I'm using the iPad Pro exactly how it came out of the box.