How does a cross-over BJT's damp the distortion with help of negative resistive feedback in an analog audio amplifier?
Indeed you get (almost) no distortion at the output because it is suppressed by the loopgain. You do see distortion (actually pre-distortion) at the output of the opamp. The opamp is compensating for the distortion of the output stage.

It is unclear how large the gain of your opamp (model) is but my guess is that it is very high (> 1000) that results in a high loopgain and thus high suppression of the distortion.

So lower the gain of the opamp to 10 or 100 and see what happens.

Pro tip:
Don't use a triangle wave as input signal but a sinewave then plot the spectrum (use FFT function) of the signals. That way you can get more accurate / insightful numbers for the distortion and also "see" lower distortion values. For example 1% THD is impossible to see in a time plot but shows up in a spectral plot as peaks up to -40 dBc.