I think from Season 3 to mid-season 5 and then late season 7 of TNG, most of DS9, and a couple seasons of Voyager, this isn't true. I think people knew at the time we had genuinely good Trek on the air.
The OP’s point is that there were old fans gatekeeping and downtalking ‘NuTrek’ pretty much since fan organizations took out full page newspaper ads in the US trying to stop TAS from being aired.
I was going to Star Trek cons in 1990. No matter how objectively great season 3 of TNG was, many TOS diehards were still campaigning against it.
Longstanding TOS fans could still be pretty toxic at that point to new TNG fans in person too. The guests at cons were still largely TOS cast. It was hard even to get a TNG t-shirt then.
Fast forward to 1993 and TNG cosplay was everywhere, the guests and panels were TNG and DS9 was the exciting new thing.