So were receivers such a gateway...depended whether you wanted a separate tuner or cared about radio.... Does make me somewhat curious about the timeline for such products but not too much
. Can't say the "sound" of receivers was all that different from integrated amps or separates....and still do.
If receivers were a gateway from anything, it would be from a combo unit that had the receiver & turntable or receiver, turntable and some kind of tape deck, even though they became monstrous (the Pioneer SX-1980 was over 20" wide, 20" deep, 8" high and weighed 98 pounds). Oddly, even with 270W/channel, I could never get enough output from one of those with the same model of cartridge for it to be usable, but my 30W/channel Sony integrated could do that with the volume control at 12:00.
Separates and receivers were always pretty far apart, but I'm referring to a time that was probably before your first exposure to audio equipment and any fascination with it. My first receiver was a Pioneer SX-525 that was able to put out a ground-pounding 13W/channel at 1% THD (it was tested at a McIntosh clinic). When I started college, a friend got a job at a stereo store and several of the others in the dorms had better stereos than mine and it wasn't long until I became more interested. I changed he turntable from a real POS to a better one, but it wa very prone to feedback, so putting it in a different room would have been best. Then, I upgraded my midrange drivers & woofers, cobbled together different cabinets and eventually bought a pair of speakers that I still have and enjoy.
But I digress. The typical receiver at the time didn't have pre out/power amp in unless it was close to TOTL and my receiver really was poor, it had a good tuner, so I kept it after buying my first integrated amp which was better in every way- it had more inputs, pre out/power amp in, a much better phono section, outperformed the rated power output spec by a large margin AT or below rated distortion. Also, if someone wanted to use the tone controls, they had different 'turnover' points, so they would affect the signal starting or ending at different frequencies, depending on what was needed. Also had a low and high filter, so turntable rumble and excessive hiss could be removed. Oddly, the MM phone section was capable of letting me use my moving coil cartridge, even though it wasn't the high output version. A couple of years later, I found another integrated that had similar features, but was much more powerful, had a MC preamp and was one of the first to have a PWM (Pulse Width Modulation) power supply. I kept that until only a few years ago, but hadn't ben using it because the volume control would periodically become noisy and it was a royal PITA to clean. When I got it ready to ship, I connected it and listened- my first thought was "Damn! This sounds freaking great!".
My point is that before AVRs became the norm, integrated amplifiers were the next step before going to separates- a receiver may have had a lot of power, especially after the manufacturers started their spec race, but they still weren't as good as separates, even though many integrated amps were easily as good as some very good separates. However, even if you look at the newest Sony, Yamaha and other integrated amps and compare them with what was available before about 1990, the new ones don't have the power, don't have the inputs and not all have pre out/power amp in and almost none have a MC preamp. While the last point doesn't matter to the vast majority, it was important in the past. The lack of power output is something I don't understand.
I would put some of the best integrated amps up against the receivers of the time in a listening test- I think the receivers would lose. The Dynamic Headroom spec came out during that time and receivers almost never did well. IIRC, NAD had an integrated amp that was rated for almost 3dB of dynamic headroom, which is excellent.