>Even using the original ps2 or ps3 controller with the right drivers on PCSX2 doesn't really reproduce the same smooth acceleration/brake curve of the PS2.

why not? if we're at the point of byte perfect recomp of system firmware+games, surely we could find a patch that would fix that in both pcsx2 or this project

Generic PS2-to-USB adapters ignore that part of the spec, so the PC doesn't receive these inputs at all. You'd need to build your own adapter out of Arduino or something.