If they are inferior, it's not for that reason. This has been covered in a number of previous threads, and in one the manufacturers were actually canvassed about their heaphone outs. The answer was that most manufacturers of popularly priced stereo amps take the signal from the speaker outlets. I don't know where this idea that non-vintage stuff uses cheap op amps, but it's demonstably wrong.
This refers specifically to stereo stuff. I don't know about AV amps, but I can attest that models like the Marantz SR4200/4300/4400 etc have very good headphone outs and can be bought cheaply on Ebay.