What about this thread: https://forums.launchbox-app.com/topic/33911-retroarch-input-lag-settings/
video_driver = "dispmanx" ("gl" if you require 3D acceleration or shaders. Will add one frame of input lag compared to dispmanx driver.)
video_vsync = true
video_threaded = false
video_frame_delay = 0
video_threaded = false is not set. My the odroid be an answer? Have you tried it yourself with a SNES Mini and a NES Mini or Real Hardware in comparison?