Ok, I figured this stuff out i think. Maybe it'll help some poor bastard like me. So, I Use AMD GPU. In AMD software there is analogical option to NVIDIA anti-lag feature (reflex) - "Radeon anti-lag". In most games it does more bad than good, but in Once Human it's almost fixed the issue at any fps (not only with high one). I can run the game at 150-200fps, so restricting it to about 120 with this option enabled removes horrible sluggish mouse feel.
Your mileage may vary, i believe unstable fps fps will still give sluggish mouse feel. Strange, because in other games mouse feels great even with 60-80fps.