Discussion quality is, in my experience, mostly a function of group size. Online discussions scale better than in person, but there's a limit.
One thing I do miss from the early internet was less anonymity being the norm on Usenet/forums/etc. Discussions tend to stay more civil when both parties know there's a "real" person on the other end.
Otherwise, my memory of early 90s internet supports exactly your conclusion. There may have been better opportunities for small discussions, but big ones devolved the same way they do today.
For a counterpoint, you only need to look at the cancer that is Facebook comments from people on their own name and face and a lot of bio attached. It's not the anonymity. At least not by itself.
I am remembering the same Internet. I got into lots of flame wars on comp.software-eng and before that on Compuserve and various FIDO boards.
It was never a very placid or friendly place. There was more tolerance for vigorous debate than there is now. The debate didn’t change many minds, I suppose.
I remember Usenet in the 90s being 50% interesting conversations mostly about niche topics and 50% randomly devolving into flame wars in larger communities.
Even "Eternal September" as a concept was something from around 1993/1994 right?
Same for the 2000s era online-bulletin-board. I often go to thegearpage.net and am appalled at the amount of shilling, dismissals and disrespect, but then I remember that in the 2000s the main guitar forum was Harmony Central, which was mostly kids calling other kids moms names.
EDIT: But coldtea makes a good point about some (IMO) more recent changes: tone-policing, excessive marketing. There's IMO also a different attitude towards curiosity today.