The OP main concern is sound quality. He wants to know if moder AVR will sound better than ancient, perhaps decade old AVR.
This is a complex question. If the AVR is going to be used purely as an amplifier, probably not. Most AVR use Class D amplification now. The implementation of Class D has improved dramatically from 15 years or so ago, but if your old AVR uses Class AB, it will probably sound better in the amplification section.
However, AVRs are also frequently DACs, depending upon your digital source. The DACs in AVRs have come a long way in the past decade.
Finally, there is Room Correction, which some AVRs do quite well, such as Anthem and Yamaha. The OP may view RC as a “feature “ but since it can fundamentally improve the sound, it is an important one