I found a couple of threads relating to controller issues in eduke32; they both seemed to imply the issues had been fixed in later versions. So I went to check what version I have to see if it was the latest and, it seems RetroPie is using an older version of eduke32. Both the binary, and installing from source, give me a commit version dated 2019-09-08. I presume this is for good reason? Or is it just more of an "if it ain't broke, don't fix it" approach, and using a "known good" (mostly) version?
This thread seems to detail the same problem (right-stick turning axis not recognized) and was then fixed, around April 2020. Is there a way for me to get the latest version, or does the script install one from two years ago specifically because it's the last one that works?
I've also borrowed a wired Xbox 360 controller to try in case it was something unique to my generic gamepad, but it was no different.