Is that a fair comparison? 70s receivers (always more popular in the USA than in the UK but I don't know about Aus) were a combined stereo amp and FM tuner, and that's all. Having both in one box saved a lot of space and there was zero-to-minimal performance hit.
Yes, it is a fair comparison. The ranges of receivers in the 70s mirrors the ranges of AVRs sold now. They are the bread and butter of the audio companies and performance gains should be obvious as you go up the price scale.
Putting tuners, preamplifiers, phono stages and power amplifiers in the same boxes saved money and I would hardly say there was a "zero-to-minimal" performance hit. There was always savings in the power supplies and the PSU modulation issues when the power stages were operating at high powers compromised the single box approaches.
Clearly, the same issues are not just still present, but more pronounced, with retrograde steps being the order of the day it seems.
AVRs are something else. They have to include video (first analogue, then digital) and multiple amp channels (initially 5.1, then 7.1 and sometimes 9.1) along with processing to split the channels, and now all sorts of digital processing. Playing stereo music was never the main purpose,
I beg to differ. The AVR started its life as a pure stereo receiver with the addition of component video switching (and some basic video enhancement/gain to cover losses) in the late 80s. "AV" was plastered all over such receivers. Then along came Dolby surround. Initially standalone processors were sold, then the basic processors along with 15-25W mono rear channel amplifiers integrated on board. Then remote source and volume along with switchable surround functions. More power, a few more channels (Dolby prologic, DD etc) and the modern AVR had evolved.
All that time the lower range 2 channel "Stereo only" receivers survived but the mid to upper range 2 channel receivers were long replaced by AVRs.
The trouble was, the phono stages disappeared or became token inclusions, the tuners became a sad joke, the amplification quality suffered and the overall build quality fell off a cliff. All in a race to the bottom, where previously, in the late 70s, it was a race to the top.