To be honest, I can't quite remember how this forum fit into the overall online Disney ecosystem back when I first joined (gulp) 23 years ago. I do go back to the alt.disney.disneyland and rec.arts.disney.parks era in the 1990s, and my memory of that time is significantly coloured by things such as Al Lutz's Promote Paul Pressler campaign, the talk of "declining by degrees", the Light Magic debacle, and the distinct negativity around DCA's announcement, construction, and opening. All of that fed into the Save Disney campaign which eventually forced the company's CEO to step down. I will say that the negativity around WDW (as far as I remember) began later once Pressler took control of the the parks division as a whole and into Iger's tenure, so it is possible this forum was a lot more positive.
All that is to say that I think Disney's online fan community has always had a very critical streak. I think you are right, though, that it has only really gathered steam among WDW fans more recently for various reasons. You are probably also right that there has been sneering at Universal by some Disney fans over that time. Maybe that naturally breeds some defensiveness.
That said, I don't think all of these critiques come from a need to overcorrect for the pre-opening hype. My point was not that Universal was making these statements, but that they were being made in this very thread in which we are participating. I can only speak for myself, but I honestly wondered if I was the only one not seeing what everyone else was apparently seeing when commenting on the concept art when I commented pre-opening rather than feeling the need to overcorrect for other people's praise of it. I also think it is kind of natural that people also now bring up the same sort of issues around theming they would if they were discussing a Disney park, both given how Epic has been discussed on here and the fact we are on a Disney theme park forum.