He is right in regards to PS3 sounding better then PS4.
GTA V is a really good example for that since we compare it on all three consoles.
In terms of sound quality GTA V on PS3 is really good.
Overall it is really well balanced between highs, mids and bass.
When I switched to PS4 I was shocked how much worse GTA V sounded.
The balance that I knew from the PS3 version was gone. Especially in terms of low-frequencies.
My Subwoofer literally had nothing to do. In general it sounded quite flat on PS4.
At first I thought that R* might have reduced the quality of the audio files in order to save storage space
on PS4. But now I got my PS5 and what should I say? There is a night and day difference. PS5 is way superior.
Just shoot a rocket launcher in the sky and you should hear a clear difference in terms of bass. And this is just one aspect.
Of course my speakers have not changed over the years, but I have not made a direct comparision between GTA V running on PS3 vs. the PS4 version running on PS5 yet. This is because I now own a new AVR (Denon X6700) to which I have not yet connected the PS3. Only my PS4 PRO and PS5 are connected to it at the moment.