Alright, I found a solution based on the last comment on that bug report!

Scrolling applications in plasma task switcher with G903 Lightspeed (wireless mode) is so fast that is unusable, but sudo modprobe -r hid_logitech_hidpp fix this, are these bugs all related?

Using that command turned every tiny scroll input into a full scroll. Pairing that with Solaar, disabling smooth scrolling, now everything works correctly!