I’d agree that there’s no reason to get a stand-alone 2-channel system when an AVR can also be used for stereo listening, and with all the goodies you mentioned.
The reason you don’t see stand-alone EQs much anymore is that they typically connected to tape monitor loops, and AVRs don’t have tape monitor loops anymore. These days using an outboard equalizer requires an outboard amplifier as well, and it’s connected between the AVR and amplifier.
EQs can also be connected between the pre-amp and amplifier section of an AVR, if it has pre-out and main-in jacks. A few AVRs used to have that feature (most notably Yamaha’s upper-tier AVRs), but I don’t think anyone’s offered that feature for at least 10 years now.
Many integrated amps have pre-out and main-in jacks, with which an equalizer could be connected. So at least in that regard, it could be argued that integrated amps are superior to AVRs.
Regards,
Wayne A. Pflughaupt