legend('FRESTIMATE results with Custom input',...
'Linear simulation of linsys with Custom input',...
'Location','SouthEast');
The step response of linear system you obtained using exact linearization does not
match the step response of the estimated frequency response with large input signal
amplitude. The linear model obtained using exact linearization does not match the
full nonlinear model at amplitudes large enough to deviate from the specified
operating point.